初二数学题 (1) (x-y-2)² (2)﹙2x+y+z﹚﹙2x-y-z﹚
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初二数学题 (1) (x-y-2)² (2)﹙2x+y+z﹚﹙2x-y-z﹚
初二数学题 (1) (x-y-2)² (2)﹙2x+y+z﹚﹙2x-y-z﹚
初二数学题 (1) (x-y-2)² (2)﹙2x+y+z﹚﹙2x-y-z﹚
(1) (x-y-2)²
=x²+y²+4-2xy-4x+4y
(2)﹙2x+y+z﹚﹙2x-y-z﹚
=[2x+(y+z)][2x-(y+z)]
=(2x)²-(y+z)²
=4x²-y²-2yz-z²
x²+y²-2xy-4x+4y+4 2. 4x²-(y+z)²
(1) (x-y)^2-4(x-y)+4 = x^2+y^2-2xy-4x+4y+4
(2) [2x+(y+z)] [2x-(y+z)] = 4x^2-(y+z)^2 = 4x^2-(y^2+z^2+2yz)