b) (3a – b)2 – (a – 2b)(2b – a).
b) (3a – b)2 – (a – 2b)(2b – a).
b) (3a – b)2 – (a – 2b)(2b – a)
= (3a – b)2 – [‒(a – 2b)(a ‒ 2b)]
= (3a)2 ‒ 2.3a.b + b2 + (a ‒ 2b)2
= 9a2 ‒ 6ab + b2 + a2 ‒ 4ab + 4b2
= (9a2 + a2) + (‒6ab ‒ 4ab) + (b2 + 4b2)
= 10a2 ‒ 10ab + 5b2.