已知4x^2+7x-1=3,求-12x^2-21x

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4x^2+7x-1=3
4x^2+7x=4
-12x^2-21x
=-3(4x^2+7x)
=-3*4
=-12

楼主你好
-12x^2-21x=-3(4x^2+7x)=-3(3+1)=-12