Q3 of 53 Page 73

Factorise:

(5a – 2b)2 – (2a – b)2

: Using the identity,

x2–y2 = (x + y)(x–y)


so, (5a – 2b)2 – (2a – b)2 = (5a–2b–2a + b)(5a–2b + 2a–b)


= (3a–b)(7a–3b)


= 21a2–9ab–7ab + 3b2


= 21a2–16ab + 3b2


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