题目计算:(1)(a−2)(a+1)−2a5÷a3(1)\left(a-2\right)\left(a+1\right)-2a^{5}\div a^{3}(1)(a−2)(a+1)−2a5÷a3；(2)(3x+y)(3x−y)+(2x+y)2(2)\left(3x+y\right)\left(3x-y\right)+\left(2x+y\right)^{2}(2)(3x+y)(3x−y)+(2x+y)2.知识点：多项式乘多项式章节：数与式 / 整式
