因式分解:-0.25(x+y)^2+0.81(x-y)^2

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因式分解:-0.25(x+y)^2+0.81(x-y)^2

-0.25(x+y)^2+0.81(x-y)^2
=[0.9(x-y)+0.5(x+y)][0.9(x-y)-0.5(x+y)]
=(1.4x-0.4y)(0.4x-1.4y)
=0.04(7x-2y)(2x-7y)

-0.25(x+y)^2+0.81(x-y)^2
=-0.5²(x+y)^2+0.9²(x-y)^2
=[0.9(x-y)]²-[0.5(x+y)]²
=[0.9(x-y)+0.5(x+y)]*[0.9(x-y)-0.5(x+y)]
=(1.4x-0.4y)(0.4x-1.4y)