(x-5y)(-x-5y)-(-x+5y)^2,其中x=二分之一,y=-1帮帮我解决

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(x-5y)(-x-5y)-(-x+5y)^2,其中x=二分之一,y=-1帮帮我解决
(x-5y)(-x-5y)-(-x+5y)^2,其中x=二分之一,y=-1
帮帮我解决

(x-5y)(-x-5y)-(-x+5y)^2,其中x=二分之一,y=-1帮帮我解决
(x-5y)(-x-5y)-(-x+5y)^2
=(-5y+x)(-5y-x)-x^2-25y^2+10xy
=25y^2-x^2-x^2-25y^2+10xy
=-2x^2+10xy
把x=1/2 y=-1代入
-2x^2+10xy =-2/11
解析：(-5y+x)(-5y-x) 平方差公式.
（a+b）乘（a-b）=a^2-b^2
(-x+5y)^2 完全平方

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