1²+2²+...+n²= n(n+1)(2n+1)/6.
n=5=> 1²+2²+...+5²=5(5+1)(2*5+1)/6=5*6*11/6=55
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1²+2²+...+n²= n(n+1)(2n+1)/6.
n=5=> 1²+2²+...+5²=5(5+1)(2*5+1)/6=5*6*11/6=55
S = 1 + 4 + 9 + 16 + 25
S = 5 + 9 + 16 + 25
S = 14 + 16 + 25
S = 30 + 25
S = 55