RD Sharma Solutions Class 7 Mathematics Solutions for Algebraic Expressions Exercise 7.2 in Chapter 7 - Algebraic Expressions

Question 6 Algebraic Expressions Exercise 7.2

(i) 8a – 6ab +5b, –6a – ab – 8b and –4a + 2ab + 3b

(ii) 5x3+ 7 + 6x - 5x2, 2x2 – 8 - 9x, 4x - 2x2 + 3 x 3, 3 x 3 - 9x - x2 and x - x2 - x3 – 4

(i) Given 8a – 6ab + 5b, –6a – ab – 8b and –4a + 2ab+ 3b

= (8a – 6ab + 5b) + (–6a – ab – 8b) + (–4a + 2ab + 3b)

Collecting positive and negative like terms together, we get

= 8a – 6a – 4a –6ab – ab + 2ab + 5b – 8b + 3b

= 8a – 10a – 7ab+ 2ab + 8b – 8b

= –2a – 5ab

(ii) Given 5x3 + 7 + 6x - 5x2,

2x2 – 8 - 9x, 4x - 2x2 + 3 x 3, 3 x 3 - 9x - x2 and x - x2 - x3 – 4

= (5 x 3 + 7+ 6x - 5x2) + (2 x 2 – 8 - 9x) + (4x - 2x2+ 3 x 3) + (3 x 3 - 9x-x2) + (x - x2 - x3 - 4)

Collecting positive and negative like terms together, we get

5x3 +3x3 + 3x3 - x3 - 5x2 + 2x2- 2x2- x2 - x2 + 6x - 9x + 4x - 9x + x + 7 – 8- 4

= 10x3- 7x2 - 7x – 5

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