不挂科搜题免费

问题:

(1)化简:(3x 2 ﹣5x﹣1)+(3﹣2x 2 +7x) (2)先化简,再求值:3(2x 2

答案:

(1)原式=3x 2 ﹣5x﹣1+3﹣2x 2 +7x =x 2 +2x+2; (2)原式=6x 2 ﹣3xy﹣6x 2 +4xy =xy, 当x=﹣2,y=﹣3时, 原式=(﹣2)×(﹣3)=6.