先化简,再求值(2a+1)(2a-1)-(2a-3)(3a+1),其中a=-2分之1

问题描述:

先化简,再求值(2a+1)(2a-1)-(2a-3)(3a+1),其中a=-2分之1

(2a+1)(2a-1)-(2a-3)(3a+1)
=4a^2-1-6a^2+7a+3
=-2a^2+7a+2 a=-1/2
=-2(-1/2)^2-7/2+2
=-4+2
=-2