Question

"Question 4 (a) Subtract 4a − 7ab + 3b + 12 from 12a − 9ab + 5b − 3 (b) Subtract 3xy + 5yz − 7zx from 5xy − 2yz − 2zx + 10xyz (c) Subtract 4p^2q − 3pq + 5pq^2 − 8p + 7q − 10 from 18 − 3p − 11q + 5pq − 2pq^2 + 5p^2q

Class 8 Algebraic Expressions and Identities Page 140"

Answer 1

Algebraic expressions:

A combination of constants and variables connected by any or all of the four fundamental operations +, -,×,÷ is called an algebraic expression.

Terms:

The different parts of the expression separated by the sign+ or – are called the terms of the expression.

Subtraction of algebraic expression:

While Subtracting algebraic expressions  we change the sign of the expression which is to be subtracted.

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Solution:

While subtracting, we need to remember signs are reversed after –sign once bracket is opened
ie. + becomes - and - becomes +

i) (12a - 9ab + 5b - 3) - (4a - 7ab + 3b + 12)
= 12a - 9ab + 5b - 3 - 4a + 7ab - 3b – 12

= 12a -4a-9ab+7ab +5b-3b -3-12
= 8a - 2ab + 2b – 15

ii) (5xy - 2yz - 2zx + 10xyz) - (3xy + 5yz - 7zx)
= 5xy - 2yz - 2zx + 10xyz - 3xy - 5yz + 7zx

= 5xy-3xy-2yz-5yz-2zx+7zx+10xyz

= 2xy - 7yz + 5zx + 10xyz

iii) (18 - 3p - 11q + 5pq - 2pq² + 5p²q) - (4p²q - 3pq + 5pq² - 8p + 7q - 10)

= 18 - 3p - 11q + 5pq - 2pq²+ 5p²q - 4p²q + 3pq - 5pq² + 8p - 7q + 10

=18+10-3p+8p-11q-7q+5pq+3pq-2pq²-5pq²+5p²q-4p²q

= 28 + 5p - 18q + 8pq - 7pq² + p²q

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Hope this will help you...