即:几个整式相乘 一个多项式.
①a(x+y)=ax+ay;
②x2+2xy+y2-1=x(x+2y)+(y +1)(y-1);
③ax2-9a=a(x+3)(x-3);
④x2+2+ =
⑤2a3=2a·a·a.