第3课时,多项式与多项式相乘,先用一个多项式的每一项乘另一个多项式的每一项,再把所得的积 .,相加,多项式乘多项式 【例】 计算:(1)(3x-1)(2x+1); (2)(x-3y)(x+7y); (3)(2x4-3x3+5x2+x)(-x+1). 解:(1)原式=3x2x+13x-12x-1=6x2+3x-2x-1=6x2+x-1; (2)原式=xx+x7y-3yx-3y7y=x2+4xy-21y2; (3)原式=2x4(-x)+2x41-3x3(-x)-3x31+5x2(-x)+5x21+x(-x)+x1 =-2x5+2x4+3x4-3x3-5x3+5x2-x2+x =-2x5+5x4-8x3+4x2+x.,1,2,3,4,5,6,7,1.下列各式,运算结果为a23a18的是( ) A.(a2)(a9) B.(a6)(3+a) C.(a+6)(a3) D.(a+2)(a9),答案,1,2,3,4,5,6,7,2.(2015广东佛山中考)若(x+2)(x-1)=x2+mx+n,则m+n=( ) A.1 B.-2 C.-1 D.2,答案,1,2,3,4,5,6,7,3.(2015福建福州中考)计算(x-1)(x+2)的结果是 .,答案,1,2,3,4,5,6,7,4.计算:(2x+y)(x-y)= ;(x+y)(x2-xy+y2)= .,答案,1,2,3,4,5,6,7,5.已知a+b= ,ab=1,化简(a2)(b2)的结果是 .,答案,1,2,3,4,5,6,7,6.计算: (1)(2x+3y)(3x-2y); (2)(x+2)(x1)-(x2)(x+3).,答案,1,2,3,4,5,6,7,7.把一个正方形改为长方形后,长方形的长比正方形的边长多3厘米,宽少2厘米.如果长方形的面积与正方形的面积相等,试求正方形的边长.,答案,