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(-1/4x -2y)(+1/4x-2y)

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(-1/4x -2y)(+1/4x-2y)
(-x-y-1/2a)(x+y-1/2a)
(a^2+b^2)(a+b)(a-b)
(a-2b-1)(a+2b-1)
a-2b=2,a^2-b^2=5,求a+b
(-1/4x -2y)(+1/4x-2y) =-(1/4x +2y)(1/4x-2y)=-(1/16x^2-4y^2)=4y^2-1/16x^2
(-x-y-1/2a)(x+y-1/2a) =-(x+y+1/2a)(x+y-1/2a)=-[(x+y)^2-1/4a^2]=1/4a^2-x^2-2xy-y^2
(a^2+b^2)(a+b)(a-b) =(a^2+b^2)(a^2-b^2)=a^4-b^4
(a-2b-1)(a+2b-1) =(a-1)^2-4b^2=a^2-2a+1-4b^2