If the sum of first $n$ terms of an $A.P.$ is $cn(n -1)$ , where $c \neq 0$ , then sum of the squares of these terms is
If the sum of first $n$ terms of an $A.P.$ is $cn(n -1)$ , where $c \neq 0$ , then sum of the squares of these terms is
- A
$c^2n^2(n+1)^2$
- B
$\frac{2}{3}c^2n(n-1)(2n-1)$
- C
$\frac{2}{3}c^2n(n+1)(2n+1)$
- D
$\frac{c^2 n^2}{3}(n+1)^2$
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