题目下列由左到右边的变形中,是因式分解的是（ ）A.x2−1=x(x−1x){x}^{2}-1=x(x-\frac{1}{x})x2−1=x(x−x1)B.x2−9=(x+3)(x−3)x^{2}-9=\left(x+3\right)\left(x-3\right)x2−9=(x+3)(x−3)C.x2−4+3x=(x+2)(x−2)+3xx^{2}-4+3x=\left(x+2\right)\left(x-2\right)+3xx2−4+3x=(x+2)(x−2)+3xD.(x+2)(x−2)=x2−4(x+2)\left(x-2\right)=x^{2}-4(x+2)(x−2)=x2−4知识点：十字相乘法章节：数与式 / 因式分解
