已知x²+2x-5=0,求(3x+7)(x-1)-(x-2)(x+2)的值
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已知x²+2x-5=0,求(3x+7)(x-1)-(x-2)(x+2)的值
已知x²+2x-5=0,求(3x+7)(x-1)-(x-2)(x+2)的值
已知x²+2x-5=0,求(3x+7)(x-1)-(x-2)(x+2)的值
已知x²+2x-5=0
则x²+2x=5
那么,
(3x+7)(x-1)-(x-2)(x+2)
=3x²+4x-7-x²+4
=2x²+4x-3
=2(x²+2x)-3
=2×5-3
=10-3
=7