Question
If the sum of $n$ terms of an A.P. is cn $(n-1)$, where $c \neq 0$, then sum of the squares of these terms is(A) $c^{2} n^{2}(n+1)^{2}$(B) $\frac{2}{3} c^{2} n(n-1)(2 n-1)$(C) $\frac{2 c^{2}}{3} n(n+1)(2 n+1)$(D) None of these
Step 1
Now, the $n$th term is the sum of the first $n$ terms minus the sum of the first $n-1$ terms. Hence, we have \[T_n = S_n - S_{n-1} = cn(n-1) - c(n-1)(n-2) = c(n-1)(2n-1).\] Show more…
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