If , then sum of products of 1, 2, 3, 4, ..., 20 taking two at a time is…

MATHEMATICS · Single correct · CBSE · Mathematics · Binomial Theorem · Binomial Theorem

Problem

\sum_{1}^{20} r^3 = a

\sum_{1}^{20} r^2 = b

then sum of products of 1, 2, 3, 4, ..., 20 taking two at a time is : (a)

\frac{a-b}{2}

(b)

\frac{a^2 - b^2}{2}

(c)

a-b

(d)

a^2 - b^2