分子因式分解
(x² + 4x + 4 +1) / (x+2)- (x² + 6x +9 +1)/(x+3)+ 1
= [(x+2)² +1] / (x+2) -[(x+3)² + 1]/(x+3)+ 1
= (x+2) +1/(x+2) -(x+3) - 1/(x+3) + 1
= 1/(x+2) - 1/(x+3)
= [(x+3) - (x+2)] / (x+2)(x+3)
= 1 / (x+2)(x+3)