先化简,再求值:2(x+5)(x-4)-3(x-6)(x+1),其中x=2.

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先化简,再求值:2(x+5)(x-4)-3(x-6)(x+1),其中x=2.
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先化简,再求值:2(x+5)(x-4)-3(x-6)(x+1),其中x=2.
先化简,再求值:2(x+5)(x-4)-3(x-6)(x+1),其中x=2.

先化简,再求值:2(x+5)(x-4)-3(x-6)(x+1),其中x=2.
2(x+5)(x-4)-3(x-6)(x+1)
=2(x^2+x-20)-3(x^2-5x-6)
=2x^2+2x-40-3x^2+15x+18
=-x^2+17x-22
当x=2时,-x^2+17x-22
=-2^2+17*2-22
=-4+34-22
=8

8

2(x+5)(x-4)-3(x-6)(x+1)
=2(x^2+x-20)-3(x^2-5x-6)
=2x^2+2x-40-3x^2+15x+18
=-x^2+17x-22
=-2^2+17*2-22
=-4+34-22
=8