当x=9/2时,求(x^2+7x+10)/(x^2+6x+5)×(x^3+1)/(x^2+4x+4)÷(x^2-x+1)/(x+2)

(x^2+7x+10)/(x^2+6x+5)×(x^3+1)/(x^2+4x+4)÷(x^2-x+1)/(x+2)
=(x+2)(x+5)/(x+1)(x+5)*(x+1)(x^2-x+1)/(x+2)^2÷(x^2-x+1)/(x+2)
=(x+2)(x+5)/(x+1)(x+5) * (x+1)(x^2-x+1)/(x+2)^2 * (x+2)/(x^2-x+1)
=1(x+1)(x^2-x+1)/(x+2)^2是怎么来的？我不懂！谢谢了！x^3+1=(x+1)(x^2-x+1) 依据：立方和公式，a^3+b^3=(a+b)(a^2-ab+b^2)x^2+4x+4=(x+2)^2即(x+2)² 依据：完全平方公式，(a+b)^2=a^2+2ab+b^2逆用