Page 1
Answers & Solutions
for
JEE (Main)-2023 (Online) Phase-2
(Mathematics, Physics and Chemistry)
10/04/2023
Morning
Time : 3 hrs. M.M. : 300
IMPORTANT INSTRUCTIONS:
(1) The test is of 3 hours duration.
(2) The Test Booklet consists of 90 questions. The maximum marks are 300.
(3) There are three parts in the question paper consisting of Mathematics, Physics and Chemistry
having 30 questions in each part of equal weightage. Each part (subject) has two sections.
(i) Section-A: This section contains 20 multiple choice questions which have only one correct
answer. Each question carries 4 marks for correct answer and –1 mark for wrong answer.
(ii) Section-B: This section contains 10 questions. In Section-B, attempt any five questions out
of 10. The answer to each of the questions is a numerical value. Each question carries 4 marks
for correct answer and –1 mark for wrong answer. For Section-B, the answer should be
rounded off to the nearest integer.
Page 2
Answers & Solutions
for
JEE (Main)-2023 (Online) Phase-2
(Mathematics, Physics and Chemistry)
10/04/2023
Morning
Time : 3 hrs. M.M. : 300
IMPORTANT INSTRUCTIONS:
(1) The test is of 3 hours duration.
(2) The Test Booklet consists of 90 questions. The maximum marks are 300.
(3) There are three parts in the question paper consisting of Mathematics, Physics and Chemistry
having 30 questions in each part of equal weightage. Each part (subject) has two sections.
(i) Section-A: This section contains 20 multiple choice questions which have only one correct
answer. Each question carries 4 marks for correct answer and –1 mark for wrong answer.
(ii) Section-B: This section contains 10 questions. In Section-B, attempt any five questions out
of 10. The answer to each of the questions is a numerical value. Each question carries 4 marks
for correct answer and –1 mark for wrong answer. For Section-B, the answer should be
rounded off to the nearest integer.
MATHEMATICS
SECTION - A
Multiple Choice Questions: This section contains 20
multiple choice questions. Each question has 4 choices
(1), (2), (3) and (4), out of which ONLY ONE is correct.
Choose the correct answer:
1. Let f be a differentiable function such that
( ) ( )
2
0
4
x
x f x x tf t dt -=
?
,
( )
2
1
3
f = . Then 18 f(3) is
equal to
(1) 210
(2) 160
(3) 150
(4) 180
Answer (2)
Sol.
2
0
( ) 4 ( )
x
x f x x t f t dt -=
?
Diff. w.r.t. x
2
( ) 2 ( ) 1 4 ( ) x f x x f x xf x ? + - =
?
2
( ) 1 2 ( ) x f x x f x ? - =
?
2
21 dy
y
dx x
x
-= Let ( ) ( )
dy
y f x f x
dx
??
= = ?
??
??
?
2
2ln
2
1
I.F
dx
x
x
ee
x
-
-
?
= = =
?
24
1 y
dx C
xx
=+
?
?
23
1
3
y
C
xx
= - + Now,
2
(1)
3
f =
21
33
C = - +
? 1 C =
?
2
1
()
3
f x x
x
= - +
?
1
18 (3) 18 9 160
9
f
??
= - + =
??
??
2. An arc PQ of a circle subtends a right angle at its
centre O. The mid point of the arc PQ is R. If
OP u = , OR v = and OQ u v = ? + ? , then ?, ?
2
are
the roots of the equation
(1) x
2
+ x – 2 = 0
(2) x
2
– x – 2 = 0
(3) 3x
2
– 2x – 1 = 0
(4) 3x
2
+ 2x – 1 = 0
Answer (2)
Sol.
OQ u v = ? + ?
OR v =
OP u =
? R will lie on angle bisector of and OQ OP
0 OQ OP ?=
( )
2
0 v v u = ? + ? ? ? =
? ? + ? ? cos45° = 0
?
2
-?
?=
2
1
2
OQ OR r ?=
? ( ) ( )
2
2
r
v v v ? + ? ? =
22
2
22
rr
r = ? ? + ? ? =
1
22
?
= + ? =
Page 3
Answers & Solutions
for
JEE (Main)-2023 (Online) Phase-2
(Mathematics, Physics and Chemistry)
10/04/2023
Morning
Time : 3 hrs. M.M. : 300
IMPORTANT INSTRUCTIONS:
(1) The test is of 3 hours duration.
(2) The Test Booklet consists of 90 questions. The maximum marks are 300.
(3) There are three parts in the question paper consisting of Mathematics, Physics and Chemistry
having 30 questions in each part of equal weightage. Each part (subject) has two sections.
(i) Section-A: This section contains 20 multiple choice questions which have only one correct
answer. Each question carries 4 marks for correct answer and –1 mark for wrong answer.
(ii) Section-B: This section contains 10 questions. In Section-B, attempt any five questions out
of 10. The answer to each of the questions is a numerical value. Each question carries 4 marks
for correct answer and –1 mark for wrong answer. For Section-B, the answer should be
rounded off to the nearest integer.
MATHEMATICS
SECTION - A
Multiple Choice Questions: This section contains 20
multiple choice questions. Each question has 4 choices
(1), (2), (3) and (4), out of which ONLY ONE is correct.
Choose the correct answer:
1. Let f be a differentiable function such that
( ) ( )
2
0
4
x
x f x x tf t dt -=
?
,
( )
2
1
3
f = . Then 18 f(3) is
equal to
(1) 210
(2) 160
(3) 150
(4) 180
Answer (2)
Sol.
2
0
( ) 4 ( )
x
x f x x t f t dt -=
?
Diff. w.r.t. x
2
( ) 2 ( ) 1 4 ( ) x f x x f x xf x ? + - =
?
2
( ) 1 2 ( ) x f x x f x ? - =
?
2
21 dy
y
dx x
x
-= Let ( ) ( )
dy
y f x f x
dx
??
= = ?
??
??
?
2
2ln
2
1
I.F
dx
x
x
ee
x
-
-
?
= = =
?
24
1 y
dx C
xx
=+
?
?
23
1
3
y
C
xx
= - + Now,
2
(1)
3
f =
21
33
C = - +
? 1 C =
?
2
1
()
3
f x x
x
= - +
?
1
18 (3) 18 9 160
9
f
??
= - + =
??
??
2. An arc PQ of a circle subtends a right angle at its
centre O. The mid point of the arc PQ is R. If
OP u = , OR v = and OQ u v = ? + ? , then ?, ?
2
are
the roots of the equation
(1) x
2
+ x – 2 = 0
(2) x
2
– x – 2 = 0
(3) 3x
2
– 2x – 1 = 0
(4) 3x
2
+ 2x – 1 = 0
Answer (2)
Sol.
OQ u v = ? + ?
OR v =
OP u =
? R will lie on angle bisector of and OQ OP
0 OQ OP ?=
( )
2
0 v v u = ? + ? ? ? =
? ? + ? ? cos45° = 0
?
2
-?
?=
2
1
2
OQ OR r ?=
? ( ) ( )
2
2
r
v v v ? + ? ? =
22
2
22
rr
r = ? ? + ? ? =
1
22
?
= + ? =
? 2 ?=
? ? = –1
? ? = –1, ?
2
= 2
? x
2
– x – 2 = 0
3. A line segment AB of length ? moves such that the
points A and B remain on the periphery of a circle
of radius ?. Then the locus of the point, that divides
the line segment AB in the ratio 2 : 3, is a circle of
radius
(1)
3
5
? (2)
2
3
?
(3)
19
5
? (4)
19
7
?
Answer (3)
Sol.
Let O be the origin and radius of circle is ? and AB = ?
? ( )
12
1 2 2cos = - ? - ?
? ( )
12
1
cos
2
? - ? =
?
12
2 cos 3 cos
5
h
? ? + ? ?
=
12
2 sin 3 sin
5
k
? ? + ? ?
=
? ( ) ( )
2
22
12
4 9 12 cos
25
hk
?
?? + = + + ? - ?
??
2
19
25
?
=?
? Radius 19
5
?
=
4. If the coefficient of x
7
in
13
2
1
ax
bx
??
-
??
??
and the
coefficient of x
– 5
in
13
2
1
ax
bx
??
+
??
??
are equal, then
a
4
b
4
is equal to:
(1) 11 (2) 44
(3) 22 (4) 33
Answer (3)
Sol. Coefficient of x
7
in
13
2
1
ax
bx
??
-
??
??
( )
13
13
1
2
1
9
r
r
rr
T C x
bx
-
+
??
=-
??
??
? 2 r =
? Coeff.
11
13
2
2
a
C
b
=
Similarly coeff. of x
–5
in
13
2
1
ax
bx
??
+
??
??
? 6 r =
? Coeff.
7
13
6
6
a
C
b
=
Now,
11 7
13 13
26
26
aa
CC
bb
=
? a
4
b
4
= 22
5. Let O be the origin and the position vector of the
point P be – 2 3 i j k -+ . If the position vectors of the
points A, B and C are –2 3 , 2 4 2 i j k i j k + - + - and
42 i j k - + - respectively, then the projection of the
vector OP on a vector perpendicular to the vectors
AB and AC is
(1) 3 (2)
8
3
(3)
7
3
(4)
10
3
Answer (1)
Page 4
Answers & Solutions
for
JEE (Main)-2023 (Online) Phase-2
(Mathematics, Physics and Chemistry)
10/04/2023
Morning
Time : 3 hrs. M.M. : 300
IMPORTANT INSTRUCTIONS:
(1) The test is of 3 hours duration.
(2) The Test Booklet consists of 90 questions. The maximum marks are 300.
(3) There are three parts in the question paper consisting of Mathematics, Physics and Chemistry
having 30 questions in each part of equal weightage. Each part (subject) has two sections.
(i) Section-A: This section contains 20 multiple choice questions which have only one correct
answer. Each question carries 4 marks for correct answer and –1 mark for wrong answer.
(ii) Section-B: This section contains 10 questions. In Section-B, attempt any five questions out
of 10. The answer to each of the questions is a numerical value. Each question carries 4 marks
for correct answer and –1 mark for wrong answer. For Section-B, the answer should be
rounded off to the nearest integer.
MATHEMATICS
SECTION - A
Multiple Choice Questions: This section contains 20
multiple choice questions. Each question has 4 choices
(1), (2), (3) and (4), out of which ONLY ONE is correct.
Choose the correct answer:
1. Let f be a differentiable function such that
( ) ( )
2
0
4
x
x f x x tf t dt -=
?
,
( )
2
1
3
f = . Then 18 f(3) is
equal to
(1) 210
(2) 160
(3) 150
(4) 180
Answer (2)
Sol.
2
0
( ) 4 ( )
x
x f x x t f t dt -=
?
Diff. w.r.t. x
2
( ) 2 ( ) 1 4 ( ) x f x x f x xf x ? + - =
?
2
( ) 1 2 ( ) x f x x f x ? - =
?
2
21 dy
y
dx x
x
-= Let ( ) ( )
dy
y f x f x
dx
??
= = ?
??
??
?
2
2ln
2
1
I.F
dx
x
x
ee
x
-
-
?
= = =
?
24
1 y
dx C
xx
=+
?
?
23
1
3
y
C
xx
= - + Now,
2
(1)
3
f =
21
33
C = - +
? 1 C =
?
2
1
()
3
f x x
x
= - +
?
1
18 (3) 18 9 160
9
f
??
= - + =
??
??
2. An arc PQ of a circle subtends a right angle at its
centre O. The mid point of the arc PQ is R. If
OP u = , OR v = and OQ u v = ? + ? , then ?, ?
2
are
the roots of the equation
(1) x
2
+ x – 2 = 0
(2) x
2
– x – 2 = 0
(3) 3x
2
– 2x – 1 = 0
(4) 3x
2
+ 2x – 1 = 0
Answer (2)
Sol.
OQ u v = ? + ?
OR v =
OP u =
? R will lie on angle bisector of and OQ OP
0 OQ OP ?=
( )
2
0 v v u = ? + ? ? ? =
? ? + ? ? cos45° = 0
?
2
-?
?=
2
1
2
OQ OR r ?=
? ( ) ( )
2
2
r
v v v ? + ? ? =
22
2
22
rr
r = ? ? + ? ? =
1
22
?
= + ? =
? 2 ?=
? ? = –1
? ? = –1, ?
2
= 2
? x
2
– x – 2 = 0
3. A line segment AB of length ? moves such that the
points A and B remain on the periphery of a circle
of radius ?. Then the locus of the point, that divides
the line segment AB in the ratio 2 : 3, is a circle of
radius
(1)
3
5
? (2)
2
3
?
(3)
19
5
? (4)
19
7
?
Answer (3)
Sol.
Let O be the origin and radius of circle is ? and AB = ?
? ( )
12
1 2 2cos = - ? - ?
? ( )
12
1
cos
2
? - ? =
?
12
2 cos 3 cos
5
h
? ? + ? ?
=
12
2 sin 3 sin
5
k
? ? + ? ?
=
? ( ) ( )
2
22
12
4 9 12 cos
25
hk
?
?? + = + + ? - ?
??
2
19
25
?
=?
? Radius 19
5
?
=
4. If the coefficient of x
7
in
13
2
1
ax
bx
??
-
??
??
and the
coefficient of x
– 5
in
13
2
1
ax
bx
??
+
??
??
are equal, then
a
4
b
4
is equal to:
(1) 11 (2) 44
(3) 22 (4) 33
Answer (3)
Sol. Coefficient of x
7
in
13
2
1
ax
bx
??
-
??
??
( )
13
13
1
2
1
9
r
r
rr
T C x
bx
-
+
??
=-
??
??
? 2 r =
? Coeff.
11
13
2
2
a
C
b
=
Similarly coeff. of x
–5
in
13
2
1
ax
bx
??
+
??
??
? 6 r =
? Coeff.
7
13
6
6
a
C
b
=
Now,
11 7
13 13
26
26
aa
CC
bb
=
? a
4
b
4
= 22
5. Let O be the origin and the position vector of the
point P be – 2 3 i j k -+ . If the position vectors of the
points A, B and C are –2 3 , 2 4 2 i j k i j k + - + - and
42 i j k - + - respectively, then the projection of the
vector OP on a vector perpendicular to the vectors
AB and AC is
(1) 3 (2)
8
3
(3)
7
3
(4)
10
3
Answer (1)
Sol. 23 OP i j k = - - +
43 AB i j k = + +
22 AC i j k = - + +
4 3 1
2 1 2
i j k
AB AC ?=
-
5 10 10 i j k = - +
Projection of OP on
( )
OP AB AC
AB AC
AB AC
??
?=
?
( )( )
5 2 3 2 2
5 1 4 4
i j k i j k - - + - +
=
++
= 3
6. Let the first term a and the common ratio r of a
geometric progression be positive integers. If the
sum of squares of its first three terms is 33033, then
the sum of these three terms is equal to
(1) 241 (2) 231
(3) 210 (4) 220
Answer (2)
Sol. a
2
+ a
2
r
2
+ a
2
r
4
= 33033
a
2
(1 + r
2
+ r
4
) = 33033
a
2
(1 + r
2
+ r
4
) = 3 × 7 × (11)
2
× 13
? a
2
= (11)
2
11 a =
? 1 +r
2
+ r
4
= 273
r
4
+ r
2
– 272 = 0
? r
2
= 16
4 r =
a = 11
ar = 44
ar
2
= 176
a + ar + ar
2
= 231
7. The slope of tangent at any point (x, y) on a curve
y = y(x) is
22
, 0.
2
xy
x
xy
+
? If y(2) = 0, then a value
of y(8) is
(1) 42 - (2) 23
(3) 23 - (4) 43
Answer (4)
Sol.
22
2
dy x y
dx xy
+
=
Put y = vx
dy dv
vx
dx dx
=+
11
2
dv
v x v
dx v
??
+ = +
??
??
?
2
11
2
dv v
x
dx v
??
-
=??
??
??
?
2
2
2
log 1 ln lnc
1
v dx
dv v x
x
v
= ? - - = +
-
??
?
2 2 2
2
1 y x y
k x k
x
x
??
--
= ? = ??
??
??
y(2) = 0
? k = 2
?
22
2
xy
x
-
=
Put x = 8
2
2
64
2 48
8
y
y
-
= ? =
43 y =
8. The negation of the statement
( ) ( ) ( )
~ p q q r ? ? ? is
(1) ( ) ( ) ~ p r q ??
(2) ( ) ( ) ( ) ~ ) ~ p r q ??
(3) ( ) ( ) ( ) ~ ) (~ ~ p q r ??
(4) ( ) ( ) ( ) ~ ) (~ ~ p q r ??
Answer (2)
Page 5
Answers & Solutions
for
JEE (Main)-2023 (Online) Phase-2
(Mathematics, Physics and Chemistry)
10/04/2023
Morning
Time : 3 hrs. M.M. : 300
IMPORTANT INSTRUCTIONS:
(1) The test is of 3 hours duration.
(2) The Test Booklet consists of 90 questions. The maximum marks are 300.
(3) There are three parts in the question paper consisting of Mathematics, Physics and Chemistry
having 30 questions in each part of equal weightage. Each part (subject) has two sections.
(i) Section-A: This section contains 20 multiple choice questions which have only one correct
answer. Each question carries 4 marks for correct answer and –1 mark for wrong answer.
(ii) Section-B: This section contains 10 questions. In Section-B, attempt any five questions out
of 10. The answer to each of the questions is a numerical value. Each question carries 4 marks
for correct answer and –1 mark for wrong answer. For Section-B, the answer should be
rounded off to the nearest integer.
MATHEMATICS
SECTION - A
Multiple Choice Questions: This section contains 20
multiple choice questions. Each question has 4 choices
(1), (2), (3) and (4), out of which ONLY ONE is correct.
Choose the correct answer:
1. Let f be a differentiable function such that
( ) ( )
2
0
4
x
x f x x tf t dt -=
?
,
( )
2
1
3
f = . Then 18 f(3) is
equal to
(1) 210
(2) 160
(3) 150
(4) 180
Answer (2)
Sol.
2
0
( ) 4 ( )
x
x f x x t f t dt -=
?
Diff. w.r.t. x
2
( ) 2 ( ) 1 4 ( ) x f x x f x xf x ? + - =
?
2
( ) 1 2 ( ) x f x x f x ? - =
?
2
21 dy
y
dx x
x
-= Let ( ) ( )
dy
y f x f x
dx
??
= = ?
??
??
?
2
2ln
2
1
I.F
dx
x
x
ee
x
-
-
?
= = =
?
24
1 y
dx C
xx
=+
?
?
23
1
3
y
C
xx
= - + Now,
2
(1)
3
f =
21
33
C = - +
? 1 C =
?
2
1
()
3
f x x
x
= - +
?
1
18 (3) 18 9 160
9
f
??
= - + =
??
??
2. An arc PQ of a circle subtends a right angle at its
centre O. The mid point of the arc PQ is R. If
OP u = , OR v = and OQ u v = ? + ? , then ?, ?
2
are
the roots of the equation
(1) x
2
+ x – 2 = 0
(2) x
2
– x – 2 = 0
(3) 3x
2
– 2x – 1 = 0
(4) 3x
2
+ 2x – 1 = 0
Answer (2)
Sol.
OQ u v = ? + ?
OR v =
OP u =
? R will lie on angle bisector of and OQ OP
0 OQ OP ?=
( )
2
0 v v u = ? + ? ? ? =
? ? + ? ? cos45° = 0
?
2
-?
?=
2
1
2
OQ OR r ?=
? ( ) ( )
2
2
r
v v v ? + ? ? =
22
2
22
rr
r = ? ? + ? ? =
1
22
?
= + ? =
? 2 ?=
? ? = –1
? ? = –1, ?
2
= 2
? x
2
– x – 2 = 0
3. A line segment AB of length ? moves such that the
points A and B remain on the periphery of a circle
of radius ?. Then the locus of the point, that divides
the line segment AB in the ratio 2 : 3, is a circle of
radius
(1)
3
5
? (2)
2
3
?
(3)
19
5
? (4)
19
7
?
Answer (3)
Sol.
Let O be the origin and radius of circle is ? and AB = ?
? ( )
12
1 2 2cos = - ? - ?
? ( )
12
1
cos
2
? - ? =
?
12
2 cos 3 cos
5
h
? ? + ? ?
=
12
2 sin 3 sin
5
k
? ? + ? ?
=
? ( ) ( )
2
22
12
4 9 12 cos
25
hk
?
?? + = + + ? - ?
??
2
19
25
?
=?
? Radius 19
5
?
=
4. If the coefficient of x
7
in
13
2
1
ax
bx
??
-
??
??
and the
coefficient of x
– 5
in
13
2
1
ax
bx
??
+
??
??
are equal, then
a
4
b
4
is equal to:
(1) 11 (2) 44
(3) 22 (4) 33
Answer (3)
Sol. Coefficient of x
7
in
13
2
1
ax
bx
??
-
??
??
( )
13
13
1
2
1
9
r
r
rr
T C x
bx
-
+
??
=-
??
??
? 2 r =
? Coeff.
11
13
2
2
a
C
b
=
Similarly coeff. of x
–5
in
13
2
1
ax
bx
??
+
??
??
? 6 r =
? Coeff.
7
13
6
6
a
C
b
=
Now,
11 7
13 13
26
26
aa
CC
bb
=
? a
4
b
4
= 22
5. Let O be the origin and the position vector of the
point P be – 2 3 i j k -+ . If the position vectors of the
points A, B and C are –2 3 , 2 4 2 i j k i j k + - + - and
42 i j k - + - respectively, then the projection of the
vector OP on a vector perpendicular to the vectors
AB and AC is
(1) 3 (2)
8
3
(3)
7
3
(4)
10
3
Answer (1)
Sol. 23 OP i j k = - - +
43 AB i j k = + +
22 AC i j k = - + +
4 3 1
2 1 2
i j k
AB AC ?=
-
5 10 10 i j k = - +
Projection of OP on
( )
OP AB AC
AB AC
AB AC
??
?=
?
( )( )
5 2 3 2 2
5 1 4 4
i j k i j k - - + - +
=
++
= 3
6. Let the first term a and the common ratio r of a
geometric progression be positive integers. If the
sum of squares of its first three terms is 33033, then
the sum of these three terms is equal to
(1) 241 (2) 231
(3) 210 (4) 220
Answer (2)
Sol. a
2
+ a
2
r
2
+ a
2
r
4
= 33033
a
2
(1 + r
2
+ r
4
) = 33033
a
2
(1 + r
2
+ r
4
) = 3 × 7 × (11)
2
× 13
? a
2
= (11)
2
11 a =
? 1 +r
2
+ r
4
= 273
r
4
+ r
2
– 272 = 0
? r
2
= 16
4 r =
a = 11
ar = 44
ar
2
= 176
a + ar + ar
2
= 231
7. The slope of tangent at any point (x, y) on a curve
y = y(x) is
22
, 0.
2
xy
x
xy
+
? If y(2) = 0, then a value
of y(8) is
(1) 42 - (2) 23
(3) 23 - (4) 43
Answer (4)
Sol.
22
2
dy x y
dx xy
+
=
Put y = vx
dy dv
vx
dx dx
=+
11
2
dv
v x v
dx v
??
+ = +
??
??
?
2
11
2
dv v
x
dx v
??
-
=??
??
??
?
2
2
2
log 1 ln lnc
1
v dx
dv v x
x
v
= ? - - = +
-
??
?
2 2 2
2
1 y x y
k x k
x
x
??
--
= ? = ??
??
??
y(2) = 0
? k = 2
?
22
2
xy
x
-
=
Put x = 8
2
2
64
2 48
8
y
y
-
= ? =
43 y =
8. The negation of the statement
( ) ( ) ( )
~ p q q r ? ? ? is
(1) ( ) ( ) ~ p r q ??
(2) ( ) ( ) ( ) ~ ) ~ p r q ??
(3) ( ) ( ) ( ) ~ ) (~ ~ p q r ??
(4) ( ) ( ) ( ) ~ ) (~ ~ p q r ??
Answer (2)
Sol. ( ) ( ) ( )
~ (~ ) p q q r ? ? ?
= ( ) ( )
~ ) ~ (~ p q q r ? ? ?
( ) ( ) ~ ~ ~ p q q r = ? ? ?
= ( ) ( ) ( ) ~ ~ ~ ~ ~ p q q p q r ? ? ? ? ?
= ( ) ( ) ~ ~ ~ q p r q r ?? ? ? ? ?
??
= ( ) ( ) ( ) ( )
~ ~ ~ ~ q p r q q r ? ? ? ? ?
= ( ) ( )
~ ~ ~ q p r q ? ? ?
= ( ) ( )
~ (~ ) p r q ??
9. Let two vertices of a triangle ABC be (2, 4, 6) and
(0, –2, –5), and its centroid be (2, 1, –1). If the
image of the third vertex in the plane x + 2y + 4z =
11 is (?, ?, ?), then ?? + ?? + ?? is equal to
(1) 70 (2) 76
(3) 74 (4) 72
Answer (3)
Sol. Let the vertex ‘C’ be (a, b, c)
20
24
3
a
a
++
= ? =
42
11
3
b
b
-+
= ? =
65
1 –4
3
c
c
-+
- = ? =
? C(4, 1, –4)
Image of C in x + 2y + 4z = 11
( ) 4 2 16 11
4 1 4
22
1 2 4 16 4 1
+ - -
? - ? - ? +
= = = - =
++
?
4
26
1
?-
= ? ? =
1
25
2
?-
= ? ? =
4
24
4
?+
= ? ? =
? ?? + ?? + ?? = 30 + 20 + 24
= 74
10. Let N denote the sum of the numbers obtained
when two dice are rolled. If the probability that
2
N
< N! is ,
m
n
where m and n are coprime, then
4m – 3n is equal to
(1) 6 (2) 12
(3) 10 (4) 8
Answer (4)
Sol. 2N < N!
N = 1 (not possible) ? 0
N = 2 (not possible) ? 1
N = 3 (not possible) ? 2
N = 4 (possible)
? Required probability
( ) 36 1 2
11
36 12
-+
==
? 4m – 3n
= 44 – 36
= 8
Option (4) is correct
11. A square piece of tin of side 30 cm is to be made
into a box without top by cutting a square from each
corner and folding up the flaps to form a box. If the
volume of the box is maximum, then its surface
area (in cm
2
) is equal to
(1) 800 (2) 675
(3) 1025 (4) 900
Answer (1)
Sol.
Volume = (30 – 2x)
2
·x = V(x)
( ) ( )( )
2
30 2 2 30 2 2 0
dV
x x x
dx
= - + - - =
? x = 5, x = 15 (not possible)
? Surface area = (30 – 2x) × 4 + (30 – 2x)
2
= 800 cm
2
(x = 5)
? Option (1) is correct
(30 – 2 ) cm x
x cm
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