当X=1/2,y=1/3时,求代数式：X-(X-Y)+(X+2Y)-(X+3Y)+……-(X+101Y)的值 麻烦过程详尽点~不好意思额，第一个括号里是+号。所以题目是：X-(X+Y)+(X+2Y)-(X+3Y)+……-(X+101Y)

X-(X-Y)+(X+2Y)-(X+3Y)+……-(X+101Y)
=X-X+Y+X+2Y-X-3Y+X+4Y-X-5Y……+X+100Y-X-101Y
=(X-X+Y)+(X+2Y-X-3Y)+(X+4Y-X-5Y)+……+(X+100Y-X-101Y)
=Y+(-Y)+(-Y)+……+(-Y)
=Y+(-50Y)
=-49Y
=-49×(1/3)
=-49/3

括号展开变成
x-x-y=-y
x+2y-x-3y=-y
x+4y-x-5y=-y
.
x+100y-x-101y=-y
所以-51y=-51/3=-17