2+4+6+8+10.+2n=
问题描述:
2+4+6+8+10.+2n=
答
2+4+6+8...+2n=
n(2+2n)/2=
n(n+1)
2+4+6+8+10.+2n=
2+4+6+8...+2n=
n(2+2n)/2=
n(n+1)