NCERT Solutions for Class 7 Maths - Algebraic Expressions- 1

Exercise 10.1

Q.1. Get the algebraic expressions in the following cases using variables, constants, and arithmetic operations: 
(i) Subtraction of z from y. 

Ans: y - z

(ii) One-half of the sum of numbers x and y.

Ans: (x + y)/2

(iii) The number z multiplied by itself. 

Ans: Z²

(iv) One-fourth of the product of numbers p and q. 

Ans: pq/4

(v) Numbers x and y both squared and added. 

Ans: x² + y²

(vi) Number 5 added to three times the product of m and n. 

Ans: 3mn + 5

(vii) A product of numbers y and z subtracted from 10. 

Ans: 10 - yz

(viii) Sum of numbers a and b subtracted from their product. 

Ans: ab - (a + b)

Q.2. (i) Identify the terms and their factors in the following expressions, show the terms and factors by tree diagram: 
(a) x - 3

Ans: 

(b) 1 + x + x²

^Ans: 

(c) y - y³

^Ans: 

(d) 5xy² + 7x²y

Ans: 

(e) -ab + 2b² - 3a²

^Ans: 

(b) -4x + 5y 

Ans: 
Terms: -4x, 5y
Factors: -4,x ; 5,y

(c) 5y + 3y²

Ans: 
Terms: 5y,3y²
Factors: 5, y ; 3,y,y

(d) xy + 2x²y²

Ans: 

Terms: xy, 2x²y² 
Factors: x, y ; 2x, x, y, y

(e) pq + q

Ans: 

Terms: pq, q
Factors: p, q ; q

(f) 1.2ab - 2.4b + 3.6a

Ans: 

Terms: 1,2ab.-2.4b,3 6a

Factors: 1.2.a.b ; -2.4,6 ; 3.6,a

(g)  

Ans: 

(h) 0.1 p² + 0.2q²

Ans: 
Terms: 0.1 p²,0.2q²
Factors: 0. 1,p,p, ; 0.2, q,q

Q.3. Identify the numerical coefficients of terms (other than constants) in the following expressions: 
(i) 5 - 3t²
(ii) 1 + t + t² + t²
(iii) x + 2xy + 3y
(iv) 100m + 1000n
(v) -p²q² + 7pq
(vi) 1.2a + 0.8b
(vii) 3.14 r²
(viii) 2(l + b)
(ix) 0.1y + 0.01y²

^Ans: 

Q.4. (a) Identify terms which contain x and give the coefficient of x. 
(i) y²x + y
(ii) 13y² - 8yx
(iii) x + y + 2
(iv) 5 + z + zx
(v) 1 + x + xy
(vi) 12xy² + x25
(vii) 7x + xy²

Ans: 

(b) Identify terms which contain y² and give the coefficient of y^2.
(i) 8 - xy²
(ii) 5y² + 7x
(iii) 2x²y - 15xy² + 7y²

Ans:

Q.5. Classify into monomials, binomials and trinomials: 
(i) 4y - 7x
(ii) y²
(iii) x + y - xy
(iv) 100
(v) ab - a - b
(vi) 5 - 3t
(vii) 4p²q - 4pq²
(viii) 7mn
(ix) z² - 3z + 8
(x) a² + b²
(xi) z² + z
(xii) 1 + x + x²

^Ans: 

 
Q.6. State whether a given pair of terms is of like or unlike terms: 

(i) 1,100
(ii) 
(iii) -29x, -29y
(iv) 14xy, 42 yx
(v) 4m²p, 4mp²
(vi) 12xz, 12x² z²

^Ans: 

Q.7. Identify like terms in the following: 
(a) -xy², -4yx², 8x², 2xy², 7y,  -11x²  - 100x, - 11yx, 20x²y, -6x², y, 2xy, 3x

Ans: Like terms are:

(i) -xy²,2 xy²
(ii) -4yx² , 20x²y
(iii) 8x²,-11x²,-6x² 
(iv) 7y, y
(v) -100x, 3x
(vi) -11yx, 2xy

(b) 10pq, 7p, 8q, -p²q², -7qp, -100q, -23, 12q²p², -5p², 41,2405 p, 78qp, 13p²q, qp², 701p²

^{Ans: Like terms are:}

(i) 10 pq - 7 pq,78 pq
(ii) 7p, 2405 p
(iii) 8q,- 100q
(iv) -p²q², 12p²q²
(v) -12,41
(vi) -5p²,701p² 
(vii) 13 p²q,qp²

Exercise 10.2

Q1: If m = 2, find the value of: 
(i) m - 2    
(ii) 3m - 5    
(iii) 9 - 5m
(iv) 3m² - 2m - 7
(v) 
Ans: 
(i) m - 2 = 2 - 2    [Putting m = 2]
= 0

(ii) 3m - 5 = 3 x 2 - 5     [Putting m = 2]
= 6 - 5 = 1

(iii) 9 - 5m = 9 - 5 x 2    [Putting m = 2]
= 9 - 10 = - 1

(iv) 3m² - 2m - 7
= 3(2)² - 2 (2) - 7        [Putting m = 2]
= 3 x 4 - 2 x 2 - 7
 = 12-4-7
 = 12- 11 = 1

(v)       [Putting m = 2]
= 5 - 4 = 1

Q2: If p = -2, find the value of:
(i) 4p + 7
(ii) - 3p² + 4p + 7
(iii) -2p³ - 3p² +4/7 + 7
Ans: 
(i) 4p + 7 = 4 (- 2) + 7    [Putting p= -2]
= -8 + 7 = -1

(ii) -3p²+4p + 7
= -3 (-2)²+ 4 (-2) + 7    [Putting p = - 2]
= - 3 x 4 - 8 + 7
= - 12 - 8 + 7
= -20 + 7 = -13

(iii) - 2p³ - 3p² +4p + 7
= - 2 (-2)³ - 3(-2)² + 4 (-2) + 7     [Putting p = - 2]
= -2 x(-8)-3 x4 -8 + 7
= 16-12-8 + 7
= -20 + 23 = 3

Q3: Find the value of the following expressions, when x = -1: 
(i) 2x - 7
(ii) -x + 2
(iii) x² + 2x  + 1
(iv) 2x²- x - 2
Ans: 
(i) 2x - 7 = 2 (-1) - 7      [Putting x= - 1]
= - 2 - 7 = - 9

(ii) - x + 2 = - (-1) + 2     [Putting x= - 1]
= 1 + 2 = 3

(iii) x² + 2 x + 1 = (-1)² + 2 (-1) + 1    [Putting x= - 1]
= 1 - 2 + 1
= 2 - 2 = 0

(iv) 2x²- x - 2 = 2 (-1)² - (-1) - 2     [Putting x= - 1]
= 2x1 + 1-2
= 2 + 1 - 2
= 3 - 2 = 1

Q4: If a = 2,b = -2, find the value of: 
(i) a² + b² 
(ii) a²+ab + b²
(iii) a² - b²
Ans: 
(i) a² + b² ( 2)² + (- 2)²    [Putting a = 2. b = - 2 ]
= 4 + 4 = 8

(ii) a²+ab + b² 
= (2) + ( 2) (- 2) +(-2)²   [Putting a = 2. b = - 2 ]
= 4 - 4 + 4 = 4

(iii) a² - b² = (2)² - (-2)²  [Putting a = 2,b = - 2]
= 4 - 4 = 0

Q5: When a = 0, b = -1, find the value of the given expressions: 
(i) 2a + 2b
(ii) 2a²+b²+1
(iii) 2a²b + 2ab² +ab
(iv) a²+ab+2
Ans: 
(i) 2a + 2b = 2 (0) + 2 (-1)    [Putting a - 0,b = - 1]
= 0 - 2 = -2  

(ii) 2a² + b² + 1 = 2 (0)² + (-1)² + 1      [Putting a - 0,b = - 1]
= 2 x 0 + 1+ 1 = 0 + 2 = 2

(iii) 2a²b + 2ab² + ab = 2(0)² (-1) + 2 (0 )(-1)² + (0 )(-1)     [Putting a - 0,b = - 1]
= 0 + 0 + 0 = 0

(iv) a² +ab + 2 - (0)² + (0) (-1) + 2   [Putting a - 0,b = - 1]
= 0 + 0 + 2 = 2

Q6: Simplify the expressions and find the value if x is equal to 2: 
(i) x + 7 + 4 (x- 5)
(ii) 3 (x + 2) + 5x - 7
(iii) 6x + 5 (x - 2)
(iv) 4 (2x - 1) + 3x + 11
Ans: 
(i) x + 7 + 4(x- 5) = x + 7 + 4x - 20 = x + 4 x + 7 - 20
= 5 x - 13 = 5 x 2 - 13                            [Putting x = 2]
= 10-13 = -3

(ii) 3 (x+ 2) + 5x - 7 = 3x + 6 + 5x -7 = 3x + 5x + 6 - 7
= 8x - 1 = 8 x 2-1                    [Putting x = -1]
= 16 - 1 = 15

(iii) 6x + 5 (x - 2) = 6x + 5x -10 = 11x - 10
= 11 x 2 - 10                      [Putting x = -1]
= 22 - 10 = 12

(iv) 4(2x - 1) + 3x + 11 = 8x - 4 + 3x +11 = 8x + 3a - 4 + 11
= 11a + 7 = 11 x 2 + 7 [Putting x = - 1]
= 22+7 = 29

Q7: Simplify these expressions and find their values if x = 3,a = -1, b = - 2 :
(i) 3x - 5 - x + 9
(ii) 2 - 8x + 4x + 4
(iii) 3a + 5 - 8a + 1
(iv) 10 - 3b - 4 - 5b
(v) 2a - 2b - 4 - 5 + a
Ans: 
(i) 3a - 5 - x + 9 = 3x - x - 5 + 9 = 2x + 4
= 2x3+4         [Putting a = 3]
= 6 + 4 = 10

(ii) 2 - 8x + 4x + 4 = - 8x + 4x + 2 + 4 = -4x + 6
= - 4 x 3 + 6     [Putting a = 3]
= -12 + 6 =12

(iii) 3a + 5 - 8a + 1 = 3a - 8a + 5 + 1 = - 5a + 6
= -5(- 1) + 6       [Putting a = - 1]
= 5 + 6 = 11

(iv) 10 - 3b - 4 - 5b = - 3b - 5b + 10 - 4 = -8b+6
= -8 (-2)+ 6    [Putting b = -2]
= 16 + 6 = 22

(v) 2a - 2b - 4 - 5 + a = 2a + a - 2b - 4 - 5
= 3a - 2b - 9 = 3 (-1)-2 (-2) -9    [Putting a = -1 , b = - 2]
= -3 + 4 -9 = -8

Q8: 
(i) If z = 10, find the value of z³ - 3 (z - 10).
(ii) If p = - 10, find the value of p² - 2p - 100
Ans:
(i) z³ -3(z-10) = (10)³-3(10 - 10)       [Putting z = 10]
= 1000 - 3 x 0 = 1000- 0
= 1000

(ii) p² - 2p - 100 = (-10)² - 2 (-10) - 100    (Putting p = - 10]

= 100+ 20 - 100 = 20

Q9: What should be the value of a if the value of 2x² + x - a equals to 5, when x = 0 ? 
Ans: 
Given: 2x² + x - a = 5
⇒ 2 (0)² + 0 - a = 5     [Putting x = 0]
⇒ 0 + 0 - a = 5
⇒ a = -5
Hence, the value of a is -5.

Q10: Simplify the expression and find its value when a = 5 and b = - 3: 2 (a² + ab) + 3 - ab
Ans:
Given: 2 (a² + ab) + 3 - ab
⇒ 2a² + 2ab + 3 - ab
⇒ 2a² + 2ab - ab + 3
⇒ 2a² + ab + 3
⇒ 2 (5)² + (5) (-3) + 3   [Putting a = 5 , b = -3]
⇒ 2 x 25 - 15 + 3
⇒ 50 - 15 + 3
⇒ 38