Question

s1=1,s2=1+3,s3=1+3+5.求s1+s2+s3+...s40的值

Answer 1

s1=1,s2=1+3,s3=1+3+5.

sn=1+3+5+.+(2n-1)=n²

1²+2²+3²+...+n²=n(n+1)(2n+1)/6

s1+s2+s3+...+s40

=1²+2²+3²+...+40²

=40×41×81/6

=22140