ta có: A= (x+2)*(x+3)*(x+4)*(x+5)=\(\left(\left(x+2\right)\cdot\left(x+5\right)\right)\cdot\left(\left(x+3\right)\cdot\left(x+4\right)\right)=\left(x^2+7x+10\right)\cdot\left(x^2+7x+12\right)\)
đặt t=x^2+7x+11
=> A=(t-1)*(t+1)-24=t^2-25=(t-5)*(t+5)
=> A=(x^2+7x+6)*(x^2+7x+16)