题目先化简,再求值:(x−1)(3x+1)−(x+2)2−4\left(x-1\right)\left(3x+1\right)-\left(x+2\right)^{2}-4(x−1)(3x+1)−(x+2)2−4,其中x2−3x=1x^{2}-3x=1x2−3x=1.知识点：单项式乘多项式章节：数与式 / 整式
