计算(a+b)(a-2b)-2(a+2b)(a-b); 5x(x2+2x+1)-(2x+3)(x-5

问题描述:

计算(a+b)(a-2b)-2(a+2b)(a-b); 5x(x2+2x+1)-(2x+3)(x-5
5x(x²+2x+1)-(2x+3)(x-5)

(a+b)(a-2b)-2(a+2b)(a-b);=a²-ab-2b²-2(a²+ab-2b²)=-a²-3ab+2b²5x(x2+2x+1)-(2x+3)(x-5)=5x³+10x²+5x-(2x²-7x-15)=5x³+8x²+12x+15梯形的上底长为(3m+4n)cm,下底长为(2m+5n)cm,高为(m+2n)cm,求此梯形的面积请采纳后,再求助,谢谢