(3x^2-4x+1)(3x^2+4x+1)= 2(3-5a)^2-5(3a-7)(3a+7)=
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(3x^2-4x+1)(3x^2+4x+1)= 2(3-5a)^2-5(3a-7)(3a+7)=
(3x^2-4x+1)(3x^2+4x+1)
=[(3x^2+1)-4x][(3x^2+1)+4x]
=(3x^2+1)^2-16x^2
=9x^4+6x^2+1-16x^2
=9x^4-10x^2+1
2(3-5a)^2-5(3a-7)(3a+7)
=2(5a-3)^2-5(3a-7)(3a+7)
=50a^2-60a+18-5(9a^2-49)
=50a^2-60a+18-45a^2+245
=50a^2-45a^2-60a+18+245
=5a^2-60a+263
再问: 我就是这样做、可是老师打了个错。
再答: 题目的类型
再问: 就是化简~ 已知xy=8满足x^2y-xy^2-x+y=36.求x^2+y^2的值 详细说下。
再答: x^2y-xy^2-x+y=36 xy(x-y)-(x-y)=36 (xy-1)(x-y)=36 (8-1)(x-y)=36 7(x-y)=36 x-y=36/7 (x-y)^2=1296/49 x^2+y^2-2xy=1296/49 x^2+y^2-2*8=1296/49 x^2+y^2-16=1296/49 x^2+y^2=1296/49+16 x^2+y^2=2080/49
再问: (xy-1)(x-y)=36 (xy-1)怎样得的?
再答: xy(x-y)-(x-y)=36提取公因式 (x-y) (xy-1)(x-y)=36
=[(3x^2+1)-4x][(3x^2+1)+4x]
=(3x^2+1)^2-16x^2
=9x^4+6x^2+1-16x^2
=9x^4-10x^2+1
2(3-5a)^2-5(3a-7)(3a+7)
=2(5a-3)^2-5(3a-7)(3a+7)
=50a^2-60a+18-5(9a^2-49)
=50a^2-60a+18-45a^2+245
=50a^2-45a^2-60a+18+245
=5a^2-60a+263
再问: 我就是这样做、可是老师打了个错。
再答: 题目的类型
再问: 就是化简~ 已知xy=8满足x^2y-xy^2-x+y=36.求x^2+y^2的值 详细说下。
再答: x^2y-xy^2-x+y=36 xy(x-y)-(x-y)=36 (xy-1)(x-y)=36 (8-1)(x-y)=36 7(x-y)=36 x-y=36/7 (x-y)^2=1296/49 x^2+y^2-2xy=1296/49 x^2+y^2-2*8=1296/49 x^2+y^2-16=1296/49 x^2+y^2=1296/49+16 x^2+y^2=2080/49
再问: (xy-1)(x-y)=36 (xy-1)怎样得的?
再答: xy(x-y)-(x-y)=36提取公因式 (x-y) (xy-1)(x-y)=36
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