1.

Factorise : (5x –3)2  – (5x –3) – 20(a) (5x + 8)(5x – 1) (b) (5x – 8)(5x + 1) (c) (5x – 8) (5x – 1) (d) (5x + 8)(5x + 1)

Answer»

(b) (5x - 8)(5x + 1)

(5x –3)2  – (5x –3) – 20

Let (5x - 3) = a. Then, the expression becomes

a2 - a - 20 = a2 - 5a + 4a - 20

= a(a - 5) + 4(a - 5) = (a - 5)(a + 4)

= (5x - 3 - 5)(5x - 3 + 4)

= (5x - 8)(5x + 1)



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