Page 144 - ICSE Math 6

Example 7: If x = 2, y = 4 and z = 5, then find the value of the following expressions.
x
2
2
(a) x + y – 2z (b) 2x – 2y – 5z (c) y – 12z
Solution: (a) Substitute x = 2, y = 4 and z = 5 to get:
2
2
2
2
x + y – 2z = 2 + 4 – 2 × (5)
= 4 + 16 – 10 = 10
(b) Substitute x = 2, y = 4 and z = 5 to get:
2x – 2y – 5z = 2 × 2 – 2 × 4 – 5 × 5
= 4 – 8 – 25 = –29
(c) Substitute x = 2, y = 4 and z = 5 to get:
x
2
y – 12z = 4 – 12 × 5
= 16 – 60 = –44

EXERCISE 12.2

1. Fill in the blanks.
(a) 3a × 4a = __________ (b) –2 × 2x = __________
2 3
4 5
2
5 4
(c) x y × x y = __________ (d) 5x × y x = __________
(e) –(a + b) = __________ (f) 2 + (a – b) = __________
(g) 3 + {a – (2a – 5)} = __________ (h) x − { 2 3 6}− − − = __________
2. Find the value of the following.

3

2 2
(a) 3 × 33a (b) –5 × (–41xy) (c) 0 × 11a b (d) 4ab × 4xy
7 25
2
2
(e) –8x × ab (f) –5xy × (–3ax ) (g) 5 xy × 49 y 3
2
3. Multiply the product of (a b) and 3 ab by 25 a .
5
4. Simplify. 27
(a) 2x – (3x – 5) (b) 4a + (9a + 2b)

(c) 5{2 – 3x + (4 – 5x + 3)} (d) 13 3x+ + {2y − 3x − 6y + 5x − 11 }
5. Find the value of 4a + 7 when:
(a) a = 1 (b) a = 3 (c) a = –4
6. If p = 2, q = 3 and r = –1, then find the value of the following expressions.
q
(a) pqr + 3 (b) 3p + 2q – r (c) p + r – 1
2
2
2
(d) p + qr + pq (e) 2p + 3p – 10 (f) (p + q + r) – pqr
AT A GLANCE

¾ The sum or difference of like terms is a like term whose numerical coefficient is the sum or
difference of the numerical coefficients of the given terms.
¾ Number × Monomial = (Number × Numerical coefficient of monomial) × Literal coefficient of
monomial
¾ Product of two monomial = (Product of numerical coefficients) × (Product of literal coefficients)
¾ The product of a polynomial and a number is the sum of products of the number and each term
of the polynomial.

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