[질문] ∑k제곱공식뭔가요?

2³=1³+3*1²+3*1+1.....(k+1)³=k³+3k²+3k+1.....(n+1)³=n³+3n²+3n+1양변을다더하고겹치는것을빼면(n+1)³=1³+3Σ(k=1~n)k²+3n(n+1)/2+n3Σ(k=1~n)k²=(n+1)³-n-1-3