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Mathematics
Problem
If
∑
1
20
r
3
=
a
\sum_{1}^{20} r^3 = a
∑
1
20
r
3
=
a
,
∑
1
20
r
2
=
b
\sum_{1}^{20} r^2 = b
∑
1
20
r
2
=
b
then sum of products of 1, 2, 3, 4, ..., 20 taking two at a time is : (a)
a
−
b
2
\frac{a-b}{2}
2
a
−
b
(b)
a
2
−
b
2
2
\frac{a^2 - b^2}{2}
2
a
2
−
b
2
(c)
a
−
b
a-b
a
−
b
(d)
a
2
−
b
2
a^2 - b^2
a
2
−
b
2
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