(x+2y)二次方
=x二次方+2x2y+2y二次方
=x二次方+4xy+2y二次方
（ax+b)(cx+d)
=axcx+axd+bcx+bd
ac(x)二次方+axd+bcx+bd
(x+y)(a+2b)
=xa+2xb+ya+2yb
(2a+3)(二分之三b+5)
=3ab+10a+二分之九b+15
(2x+3)(-x-1)
=-2x二次方-5x-3
(-2 m-1)(3m-2)
=-6m二次方+m+2
(x-y)二次方
=x二次方-2xy+y二次方
(-2x+3)二次方
=4x二次方-12x+9