用换元简化计算。原式=[(x+1)(x+6)][(x+2)(x+3)]+x^2 =(x^2+7x+6)(x^2+5x+6)+x^2 令m=x^2+6 ∴原式=(m+7x)(m+5x)+x2 =m^2+12xm+36x^2 =(m+6x)^2 =(x^2+6+6x)^2
