x3+5x2+7x+3
=(x³＋5x²＋4x)＋(3x＋3)
=x(x²＋5x＋4)＋3(x＋1)
=x(x＋1)(x＋4)＋3(x＋1)
=(x＋1)(x²＋4x＋3)
=(x＋1)(x＋1)(x＋3)
=(x＋1)²(x＋3)

不懂的还可以问!满意请及时采纳! O(∩_∩)O