(x-2y)2+(x+2y)(x-2y)-(x-3y)(x-y)计算结果是什么?x等于-4,y等于0.5代入后是多少
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(x-2y)^2+(x+2y) (x-2y)-(x-3y) (x-y)
= (x-2y) [ (x-2y) + (x+2y) ] - (x-3y) (x-y)
= (x-2y) 2x - (x-3y) (x-y)
= 2x^2 - 4xy - x^2 +4xy - 3y^2
= x^2 - 3y^2
代入后 = (-4)^2 - 3 * 0.5^2 = 16 - 3/4 = 15 1/4 =15.25
= (x-2y) [ (x-2y) + (x+2y) ] - (x-3y) (x-y)
= (x-2y) 2x - (x-3y) (x-y)
= 2x^2 - 4xy - x^2 +4xy - 3y^2
= x^2 - 3y^2
代入后 = (-4)^2 - 3 * 0.5^2 = 16 - 3/4 = 15 1/4 =15.25
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