Ta có: \(x^4+8x^2-9=x^4+9x^2-x^2-9=\left(x^4+9x^2\right)-\left(x^2+9\right)=x^2\left(x^2+9\right)-\left(x^2+9\right)=\left(x^2+9\right)\left(x^2-1\right)=\left(x^2+9\right)\left(x-1\right)\left(x+1\right)\)
b) \(x^4+5x-6\)
\(=x^4+6x-x-6\)
\(=\left(x^4-x\right)+\left(6x-6\right)\)
\(=x.\left(x^3-1\right)+6.\left(x-1\right)\)
\(=x.\left(x-1\right).\left(x^2+x+1\right)+6.\left(x-1\right)\)
\(=\left(x-1\right).\left[x.\left(x^2+x+1\right)+6\right]\)
\(=\left(x-1\right).\left(x^3+x^2+x+6\right)\)
Chúc bạn học tốt!
