当x=1,y=-2时,代数式x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
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当x=1,y=-2时,代数式x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
当x=1,y=-2时,代数式x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
当x=1,y=-2时,代数式x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
=x-x-y+x+2y-x-3y+.-x-99y
=-50y
=100
x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
=x-x-y+x+2y-x-3y+...-x-99y
=x-x+x-x...-x-y+(2y-3y)+...+(98y-99y)
=-x-y-y×98÷2
=-x-50y
=-1-50×(-2)
=99
x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
=[x-(x+y)]+[(x+2y)-(x+3Y)]+……[(x+98y)-(x+99y) ] 分成50组
=-y-y……-y
=-50y
=100
x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
=[x-(x+y)]+[(x+2y)-(x+3Y)]+……[(x+98y)-(x+99y)]
=-50y
当x=1,y=-2时
原式=100
因为该多项式一共一百项,所以含X的项前面系数为0.而含y的奇数项为负,偶数项为正,它前面的系数为(-1)+(-3)+(-5)+、、、、、、(-99) +(2+4+6+、、、、、、98)
= 运用等差数列求和公式,你自己会算。
x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
=-y*50
=100
(-y个数为y前系数+1的一半 可以找规律得到)
(x-[,x+y.])+[(x+2y)-x+3y]一直减下去
x-(x+y)+(x+2y)-(x+3Y)+……-(x+99y)
=[x-(x+y)]+[(x+2y)-(x+3Y)]+……[(x+98y)-(x+99y)]
=-50y
当x=1,y=-2时
原式=100