Prove the following identities :
(i) (a+b)2=a2+b2+2ab
(ii) (a−b)2=a2+b2−2ab [2 MARKS]
Proof: 1 Mark each
(i) (a+b)2=(a+b)(a+b)
=a2+ab+ba+b2
=a2+ab+ab+b2[ab=ba]
=a2+b2+2ab
⇒(a+b)2=a2+b2+2ab
(ii)(a−b)2=(a−b)(a−b)
=a2−ba−ab+b2
=a2−ab−ab+b2[ab=ba]
=a2+b2−2ab
⇒(a−b)2=a2+b2−2ab