计算: ①(a+b)(a-2b)-(a+2b)(a-b) ②5x(x2+2x+1)-(2x+3)(x-5)

问题描述:

计算:
①(a+b)(a-2b)-(a+2b)(a-b)   
②5x(x2+2x+1)-(2x+3)(x-5)

①原式=a2-2ab+ab-2b2-a2+ab-2ab+2b2
=-2ab;                         
②原式=5x3+10x2+5x-2x2+10x-3x+15
=5x3+8x2+12x+15.