Question

这个东西怎么算 />

Answer 1

等式左边 = (i-i+1)+((i+1)-i+1)+((i+2)-i+1)+.+(N-1-i+1)

= (i+(i+1)+(i+2)+.+N-1)+(N-1-i+1)(1-i)

=(i+(N-1))*(N-i)/2+(N-i)(1-i)

=(i+N-1+2-2i)*(N-i)/2

=(N-i+1)(N-i)/2 = 等式右边