Question

1+2+3+4+5+.+N=N(N+1)/2公式推导过程请详细写出来.

Answer 1

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=(1+n)+(2+n-1)+(3+n-2)+...+(n/2+1)

=(1+n)+(1+n)+(1+n)+...+1/2(n+1)

=n/2(1+n)+1/2(1+n)

=n(1+n)/2