1樓：數學新綠洲
1/(x-5y)－1/(x-6y)－1/(x-8y)＋1/(x-9y)
=1/(x-5y)－1/(x-8y)＋1/(x-9y)－1/(x-6y)
=[(x-8y)-(x-5y)]/[(x-5y)(x-8y)]+[(x-6y)-(x-9y)]/[(x-9y)(x-6y)]
=(-3y)/[(x-5y)(x-8y)]+ 3y/[(x-9y)(x-6y)]
=3y*
=3y*[(x-5y)(x-8y) - (x-9y)x-6y)]/[(x-9y)(x-6y)(x-5y)(x-8y)]
=3y*[(x²-13xy+40y²)-(x²-15xy+54y²)]/[(x-9y)(x-6y)(x-5y)(x-8y)]
=3y*(2xy-14y²)/[(x-9y)(x-6y)(x-5y)(x-8y)]
=6y²(x-7y)/[(x-9y)(x-6y)(x-5y)(x-8y)]
2樓：匿名使用者
1/x-5y-1/x+6y-1/x+8y+1/x-9y =(2/x-2/x)+(6y-5y+8y-9y) =0
3樓：周義
解：2x-6y/x^2-9y^2 =2（x-3y）/（x-3y）（x+3y）=2/（x+3y）2x+6y+1=0 2x+6y=-1x+3y=-1/2那麼2/（x+3y）=2÷（-1/2）=-4
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