a.\(\left(x^2+x\right)^2+3\left(x^2+x\right)+2=\left(x^2+x\right)^2+2\left(x^2+x\right)+\left(x^2+x+2\right)\)
\(=\left(x^2+x\right)\left(x^2+x+2\right)+\left(x^2+x+2\right)=\left(x^2+x+2\right)\left(x^2+x+1\right)\)
b. \(x\left(x+1\right)\left(x+2\right)\left(x+3\right)+1=\left[x\left(x+3\right)\right]\left[\left(x+1\right)\left(x+2\right)\right]+1\)
\(=\left(x^2+3x\right)\left(x^2+3x+2\right)+1\)(1)
Đặt \(t=x^2+3x\)
(1) \(\Leftrightarrow t\left(t+2\right)+1\)
\(=t^2+2t+1=\left(t+1\right)^2\)(2)
Thay \(t=x^2+3x\)vào (2) t/có:
\(\left(t+1\right)^2=\left(x^2+3x+1\right)^2\)
c. dài lắm mình lười làm, bn bấm thử mạng tìm ik nhớ tíck cho mình nha thanks
c) ab(a+b)+bc(b+c)+ac(c+a)+3abc
= ab(a+b)+abc+bc(b+c)+abc+ac(a+c)+abc
=ab(a+b+c)+bc(b+c+a)+ac(a+c+b)
=(a+b+c)(ab+bc+ac)