Which of the following equations are correct?
(i) (a+b+c)2=a2+b2+c2−2(ab+bc+ca)
(ii) (a+b)3=a3+b3+3ab(a−b)
(iii) (a−b)3=a3−b3−3ab(a+b)
(iv) a2−b2=(a+b)(a−b)
(iv) only
Using identities
(a+b+c)2=a2+b2+c2+2(ab+bc+ca)
(a+b)3=a3+b3+3ab(a+b)
(a−b)3=a3−b3−3ab(a−b)
a2−b2=(a+b)(a−b)