先化简,在求值:(ab-2)(ab+2)-(2ab-1)(ab+1)+a^2b^2=?其中a=-2,b=3
问题描述:
先化简,在求值:(ab-2)(ab+2)-(2ab-1)(ab+1)+a^2b^2=?其中a=-2,b=3
答
(ab-2)(ab+2)-(2ab-1)(ab+1)+a^2b^2=a²b²-4-【2a²b²+2ab-ab-1】+a²b²=a²b²-4-2a²b²-ab+1+a²b²= -3-ab当a=-2,b=3时上式= -3-(-2)×3= -3+6=3