先化简,再求值:2(x+5)(x-4)-3(x-6)(x+1),其中x=2.
问题描述:
先化简,再求值:2(x+5)(x-4)-3(x-6)(x+1),其中x=2.
答
2(x+5)(x-4)-3(x-6)(x+1),
=2(x2+x-20)-3(x2-5x-6),
=2x2+2x-40-3x2+15x+18,
=-x2+17x-22,
当x=2时,原式=-4+17×2-22=8.