1.计算 (1) (5x-2y)^2+20xy
=25x^2-20xy+4y^2+20xy
=25x^2+4y^2
(2)(x-3)^2(x+3)^2
=(x^2-9)^2
=x^4-18x^2+81
(3) (3x-5)^2-(2x+7)^2
=(3x-5+2x+7)(3x-5-2x-7)
=(5x-2)(x-12)
=5x^2-60x-2x+24
=5x^2-62x+24
(4)(x+y+1)(x+y-1)
=(x+y)^2-1
=x^2+2xy+y^2-1
(5)89.8^2
=(90-0.2)^2
=8100-36+0.04
=8064.04
(6)47^2-94×27+27^2
=(47-27)^2
=20^2
=400
1.计算 (1) (5x-2y)^2+20xy (2)(x-3)^2(x+3)^2 (3) (3x-5)^2-(2x+7)^2 (4)(x+y+1)
1.计算 (1) (5x-2y)^2+20xy (2)(x-3)^2(x+3)^2 (3) (3x-5)^2-(2x+7)^2 (4)(x+y+1)
1.计算 (1) (5x-2y)^2+20xy (2)(x-3)^2(x+3)^2
(3) (3x-5)^2-(2x+7)^2 (4)(x+y+1)(x+y-1)
(5)89.8^2 (6)47^2-94×27+27^2
1.计算 (1) (5x-2y)^2+20xy (2)(x-3)^2(x+3)^2
(3) (3x-5)^2-(2x+7)^2 (4)(x+y+1)(x+y-1)
(5)89.8^2 (6)47^2-94×27+27^2
数学人气:968 ℃时间:2019-10-18 03:04:56
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