Page 1
Question:1
Three angles of a quadrilateral are 75°, 90° and 75°. Find the measure of the fourth angle.
Solution:
Given: Three angles of a quadrilateral are 75°, 90° and 75°.
Let the fourth angle be x.
Using angle sum property of quadrilateral,
75°+90°+75°+x = 360° ? 240°+x = 360°
? x = 360°-240° ? x = 120°
So, the measure of the fourth angle is 120°
.
Question:2
The angles of a quadrilateral are in the ratio 2: 4 : 5 : 7. Find the angles.
Solution:
Let ?
A = 2x
°
?.
Then ?
B = (4x)
°
; ?
C = (5x)
°
and ?
D = (7x)
°
Since the sum of the angles of a quadrilateral is 360
o
, we have:
2x + 4x + 5x + 7x = 360
°
? 18 x = 360
°
? ? x = 20
°
? ?
A = 40
°
; ?
B = 80
°
; ?
C = 100
°
; ?
D = 140
°
Question:3
In the adjoining figure, ABCD is a trapezium in which AB || DC. If ?A = 55° and ?B = 70°, find ?C and ?D.
Solution:
We have AB || DC.
? A and
? D are the interior angles on the same side of transversal line AD, whereas
Page 2
Question:1
Three angles of a quadrilateral are 75°, 90° and 75°. Find the measure of the fourth angle.
Solution:
Given: Three angles of a quadrilateral are 75°, 90° and 75°.
Let the fourth angle be x.
Using angle sum property of quadrilateral,
75°+90°+75°+x = 360° ? 240°+x = 360°
? x = 360°-240° ? x = 120°
So, the measure of the fourth angle is 120°
.
Question:2
The angles of a quadrilateral are in the ratio 2: 4 : 5 : 7. Find the angles.
Solution:
Let ?
A = 2x
°
?.
Then ?
B = (4x)
°
; ?
C = (5x)
°
and ?
D = (7x)
°
Since the sum of the angles of a quadrilateral is 360
o
, we have:
2x + 4x + 5x + 7x = 360
°
? 18 x = 360
°
? ? x = 20
°
? ?
A = 40
°
; ?
B = 80
°
; ?
C = 100
°
; ?
D = 140
°
Question:3
In the adjoining figure, ABCD is a trapezium in which AB || DC. If ?A = 55° and ?B = 70°, find ?C and ?D.
Solution:
We have AB || DC.
? A and
? D are the interior angles on the same side of transversal line AD, whereas
? B and
? C are the interior angles on the same side of transversal line BC.
Now,
?A +
?D = 180
°
?
?D = 180
°
-
?A
?
? D = 180
°
- 55
°
= 125
°
Again ,
? B +
?C = 180
°
?
?C = 180
°
-
?B
?
? C = 180
°
- 70
°
= 110
°
Question:4
In the adjoining figure, ABCD is a square and ?EDC is an equilateral triangle. Prove that
i AE = BE,
ii ?DAE = 15°.
Solution:
Given: ABCD is a square in which AB = BC = CD = DA. ?EDC is an equilateral triangle in which ED = EC = DC and
? EDC =
? DEC =
? ?DCE = 60
°
.
To prove: AE = BE and
?DAE = 15
°
? Proof: In ?ADE and ?BCE, we have:
AD = BC
Sidesofasquare
DE = EC ?
Sidesofanequilateraltriangle
?ADE =
?BCE = 90
°
+ 60
°
= 150
°
?
? ?ADE ? ?BCE
i.e., AE = BE
Now,
?ADE = 150
°
Page 3
Question:1
Three angles of a quadrilateral are 75°, 90° and 75°. Find the measure of the fourth angle.
Solution:
Given: Three angles of a quadrilateral are 75°, 90° and 75°.
Let the fourth angle be x.
Using angle sum property of quadrilateral,
75°+90°+75°+x = 360° ? 240°+x = 360°
? x = 360°-240° ? x = 120°
So, the measure of the fourth angle is 120°
.
Question:2
The angles of a quadrilateral are in the ratio 2: 4 : 5 : 7. Find the angles.
Solution:
Let ?
A = 2x
°
?.
Then ?
B = (4x)
°
; ?
C = (5x)
°
and ?
D = (7x)
°
Since the sum of the angles of a quadrilateral is 360
o
, we have:
2x + 4x + 5x + 7x = 360
°
? 18 x = 360
°
? ? x = 20
°
? ?
A = 40
°
; ?
B = 80
°
; ?
C = 100
°
; ?
D = 140
°
Question:3
In the adjoining figure, ABCD is a trapezium in which AB || DC. If ?A = 55° and ?B = 70°, find ?C and ?D.
Solution:
We have AB || DC.
? A and
? D are the interior angles on the same side of transversal line AD, whereas
? B and
? C are the interior angles on the same side of transversal line BC.
Now,
?A +
?D = 180
°
?
?D = 180
°
-
?A
?
? D = 180
°
- 55
°
= 125
°
Again ,
? B +
?C = 180
°
?
?C = 180
°
-
?B
?
? C = 180
°
- 70
°
= 110
°
Question:4
In the adjoining figure, ABCD is a square and ?EDC is an equilateral triangle. Prove that
i AE = BE,
ii ?DAE = 15°.
Solution:
Given: ABCD is a square in which AB = BC = CD = DA. ?EDC is an equilateral triangle in which ED = EC = DC and
? EDC =
? DEC =
? ?DCE = 60
°
.
To prove: AE = BE and
?DAE = 15
°
? Proof: In ?ADE and ?BCE, we have:
AD = BC
Sidesofasquare
DE = EC ?
Sidesofanequilateraltriangle
?ADE =
?BCE = 90
°
+ 60
°
= 150
°
?
? ?ADE ? ?BCE
i.e., AE = BE
Now,
?ADE = 150
°
DA = DC
Sidesofasquare
DC = DE
Sidesofanequilateraltriangle
So, DA = DE
?ADE and ?BCE are isosceles triangles.
i.e.,
?DAE =
?DEA =
1
2
(180° - 150°) =
30°
2
= 15°
Question:5
In the adjoining figure, BM ? AC and DN ? AC. If BM = DN, prove that AC bisects BD.
Solution:
Given: A quadrilateral ABCD, in which BM ?? AC and DN ? AC and BM = DN.
To prove: AC bisects BD; or DO = BO
Proof:
Let AC and BD intersect at O.
Now, in ?OND and ?OMB, we have:
?OND = ?OMB (90
o
each)
?DON = ? BOM
Verticallyoppositeangles
Also, DN = BM
Given
i.e., ?OND ? ?OMB AAScongurencerule
? OD = OB
CPCT
?Hence, AC bisects BD.
Question:6
In the given figure, ABCD is a quadrilateral in which AB = AD and BC = DC. Prove that
i
AC bisects ?A and ?C,
ii BE = DE,
iii ?ABC = ?ADC.
Page 4
Question:1
Three angles of a quadrilateral are 75°, 90° and 75°. Find the measure of the fourth angle.
Solution:
Given: Three angles of a quadrilateral are 75°, 90° and 75°.
Let the fourth angle be x.
Using angle sum property of quadrilateral,
75°+90°+75°+x = 360° ? 240°+x = 360°
? x = 360°-240° ? x = 120°
So, the measure of the fourth angle is 120°
.
Question:2
The angles of a quadrilateral are in the ratio 2: 4 : 5 : 7. Find the angles.
Solution:
Let ?
A = 2x
°
?.
Then ?
B = (4x)
°
; ?
C = (5x)
°
and ?
D = (7x)
°
Since the sum of the angles of a quadrilateral is 360
o
, we have:
2x + 4x + 5x + 7x = 360
°
? 18 x = 360
°
? ? x = 20
°
? ?
A = 40
°
; ?
B = 80
°
; ?
C = 100
°
; ?
D = 140
°
Question:3
In the adjoining figure, ABCD is a trapezium in which AB || DC. If ?A = 55° and ?B = 70°, find ?C and ?D.
Solution:
We have AB || DC.
? A and
? D are the interior angles on the same side of transversal line AD, whereas
? B and
? C are the interior angles on the same side of transversal line BC.
Now,
?A +
?D = 180
°
?
?D = 180
°
-
?A
?
? D = 180
°
- 55
°
= 125
°
Again ,
? B +
?C = 180
°
?
?C = 180
°
-
?B
?
? C = 180
°
- 70
°
= 110
°
Question:4
In the adjoining figure, ABCD is a square and ?EDC is an equilateral triangle. Prove that
i AE = BE,
ii ?DAE = 15°.
Solution:
Given: ABCD is a square in which AB = BC = CD = DA. ?EDC is an equilateral triangle in which ED = EC = DC and
? EDC =
? DEC =
? ?DCE = 60
°
.
To prove: AE = BE and
?DAE = 15
°
? Proof: In ?ADE and ?BCE, we have:
AD = BC
Sidesofasquare
DE = EC ?
Sidesofanequilateraltriangle
?ADE =
?BCE = 90
°
+ 60
°
= 150
°
?
? ?ADE ? ?BCE
i.e., AE = BE
Now,
?ADE = 150
°
DA = DC
Sidesofasquare
DC = DE
Sidesofanequilateraltriangle
So, DA = DE
?ADE and ?BCE are isosceles triangles.
i.e.,
?DAE =
?DEA =
1
2
(180° - 150°) =
30°
2
= 15°
Question:5
In the adjoining figure, BM ? AC and DN ? AC. If BM = DN, prove that AC bisects BD.
Solution:
Given: A quadrilateral ABCD, in which BM ?? AC and DN ? AC and BM = DN.
To prove: AC bisects BD; or DO = BO
Proof:
Let AC and BD intersect at O.
Now, in ?OND and ?OMB, we have:
?OND = ?OMB (90
o
each)
?DON = ? BOM
Verticallyoppositeangles
Also, DN = BM
Given
i.e., ?OND ? ?OMB AAScongurencerule
? OD = OB
CPCT
?Hence, AC bisects BD.
Question:6
In the given figure, ABCD is a quadrilateral in which AB = AD and BC = DC. Prove that
i
AC bisects ?A and ?C,
ii BE = DE,
iii ?ABC = ?ADC.
Solution:
Given: ABCD is a quadrilateral in which AB = AD and BC = DC
i
In ?ABC and ?ADC, we have:
AB = AD Given
BC = DC Given
AC is common.
i.e., ?ABC ? ?ADC SSScongruencerule
? ?BAC = ?DAC and ?BCA = ?D ?CA ByCPCT
Thus, AC bisects ?A and ? C.
ii
Now, in ?ABE and ?ADE, we have:
AB = AD Given
?BAE = ?DAE ? Provenabove
AE is common.
? ?ABE ? ?ADE SAScongruencerule
? BE = DE
ByCPCT
iii ?ABC ? ?ADC Provenabove
? ?ABC = ?AD ?C ByCPCT
Question:7
In the given figure, ABCD is a square and ?PQR = 90°. If PB = QC = DR, prove that
i QB = RC,
ii PQ = QR,
iii QPR = 45°.
Solution:
Given: ABCD is a square and ?PQR = 90°.
Also, PB = QC = DR
i
We have:
BC = CD Sidesofsquare
CQ = DR Given
BC = BQ + CQ
? CQ = BC - BQ
? DR = BC - BQ ...i
Page 5
Question:1
Three angles of a quadrilateral are 75°, 90° and 75°. Find the measure of the fourth angle.
Solution:
Given: Three angles of a quadrilateral are 75°, 90° and 75°.
Let the fourth angle be x.
Using angle sum property of quadrilateral,
75°+90°+75°+x = 360° ? 240°+x = 360°
? x = 360°-240° ? x = 120°
So, the measure of the fourth angle is 120°
.
Question:2
The angles of a quadrilateral are in the ratio 2: 4 : 5 : 7. Find the angles.
Solution:
Let ?
A = 2x
°
?.
Then ?
B = (4x)
°
; ?
C = (5x)
°
and ?
D = (7x)
°
Since the sum of the angles of a quadrilateral is 360
o
, we have:
2x + 4x + 5x + 7x = 360
°
? 18 x = 360
°
? ? x = 20
°
? ?
A = 40
°
; ?
B = 80
°
; ?
C = 100
°
; ?
D = 140
°
Question:3
In the adjoining figure, ABCD is a trapezium in which AB || DC. If ?A = 55° and ?B = 70°, find ?C and ?D.
Solution:
We have AB || DC.
? A and
? D are the interior angles on the same side of transversal line AD, whereas
? B and
? C are the interior angles on the same side of transversal line BC.
Now,
?A +
?D = 180
°
?
?D = 180
°
-
?A
?
? D = 180
°
- 55
°
= 125
°
Again ,
? B +
?C = 180
°
?
?C = 180
°
-
?B
?
? C = 180
°
- 70
°
= 110
°
Question:4
In the adjoining figure, ABCD is a square and ?EDC is an equilateral triangle. Prove that
i AE = BE,
ii ?DAE = 15°.
Solution:
Given: ABCD is a square in which AB = BC = CD = DA. ?EDC is an equilateral triangle in which ED = EC = DC and
? EDC =
? DEC =
? ?DCE = 60
°
.
To prove: AE = BE and
?DAE = 15
°
? Proof: In ?ADE and ?BCE, we have:
AD = BC
Sidesofasquare
DE = EC ?
Sidesofanequilateraltriangle
?ADE =
?BCE = 90
°
+ 60
°
= 150
°
?
? ?ADE ? ?BCE
i.e., AE = BE
Now,
?ADE = 150
°
DA = DC
Sidesofasquare
DC = DE
Sidesofanequilateraltriangle
So, DA = DE
?ADE and ?BCE are isosceles triangles.
i.e.,
?DAE =
?DEA =
1
2
(180° - 150°) =
30°
2
= 15°
Question:5
In the adjoining figure, BM ? AC and DN ? AC. If BM = DN, prove that AC bisects BD.
Solution:
Given: A quadrilateral ABCD, in which BM ?? AC and DN ? AC and BM = DN.
To prove: AC bisects BD; or DO = BO
Proof:
Let AC and BD intersect at O.
Now, in ?OND and ?OMB, we have:
?OND = ?OMB (90
o
each)
?DON = ? BOM
Verticallyoppositeangles
Also, DN = BM
Given
i.e., ?OND ? ?OMB AAScongurencerule
? OD = OB
CPCT
?Hence, AC bisects BD.
Question:6
In the given figure, ABCD is a quadrilateral in which AB = AD and BC = DC. Prove that
i
AC bisects ?A and ?C,
ii BE = DE,
iii ?ABC = ?ADC.
Solution:
Given: ABCD is a quadrilateral in which AB = AD and BC = DC
i
In ?ABC and ?ADC, we have:
AB = AD Given
BC = DC Given
AC is common.
i.e., ?ABC ? ?ADC SSScongruencerule
? ?BAC = ?DAC and ?BCA = ?D ?CA ByCPCT
Thus, AC bisects ?A and ? C.
ii
Now, in ?ABE and ?ADE, we have:
AB = AD Given
?BAE = ?DAE ? Provenabove
AE is common.
? ?ABE ? ?ADE SAScongruencerule
? BE = DE
ByCPCT
iii ?ABC ? ?ADC Provenabove
? ?ABC = ?AD ?C ByCPCT
Question:7
In the given figure, ABCD is a square and ?PQR = 90°. If PB = QC = DR, prove that
i QB = RC,
ii PQ = QR,
iii QPR = 45°.
Solution:
Given: ABCD is a square and ?PQR = 90°.
Also, PB = QC = DR
i
We have:
BC = CD Sidesofsquare
CQ = DR Given
BC = BQ + CQ
? CQ = BC - BQ
? DR = BC - BQ ...i
Also, CD = RC+ DR
? DR = CD - RC = BC - RC ...ii
From i
and ii
, we have:
BC - BQ = ?BC - RC
? BQ = RC
ii
In ?RCQ and ?QBP, we have:
PB = QC Given
BQ = RC Provenabove
?RCQ = ?QBP (90
o
each)
i.e., ?RCQ ? ?QBP SAScongruencerule
? QR = PQ ByCPCT
iii
?RCQ ? ?QBP and QR = PQ Provenabove
? In ?RPQ, ?QPR = ?QRP =
1
2
(180° - 90°) =
90°
2
= 45
°
Question:8
If O is a point within a quadrilateral ABCD, show that OA + OB + OC + OD > AC + BD.
Solution:
Let ABCD be a quadrilateral whose diagonals are AC and BD and O is any point within the quadrilateral.
Join O with A, B, C, and D.
We know that the sum of any two sides of a triangle is greater than the third side.
So, in ?AOC, OA + OC > AC
Also, in ? BOD, OB + OD > BD
Adding these inequalities, we get:
(OA + OC) + (OB + OD) > (AC + BD)
? OA + OB + OC + OD > AC + BD
Question:9
In the adjoining figure, ABCD is a quadrilateral and AC is one of its diagonals. Prove that:
i
AB + BC + CD + DA > 2AC
ii
AB + BC + CD > DA
iii
AB + BC + CD + DA > AC + BD
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