\(x^4+4x^2-5\)
\(=x^4-x^3+x^3-x^2+x^2+4x^2-5\)
\(=\left(x^4-x^3\right)+\left(x^3-x^2\right)+\left(5x^2-5\right)\)
\(=x^3\left(x-1\right)+x^2\left(x-1\right)+5\left(x^2-1\right)\)
\(=x^3\left(x-1\right)+x^2\left(x-1\right)+5\left(x-1\right)\left(x+1\right)\)
\(=\left(x-1\right)\left(x^3+x^2+5x+5\right)\)
\(=\left(x-1\right)\left[x^2\left(x+1\right)+5\left(x+1\right)\right]\)
\(=\left(x-1\right)\left(x+1\right)\left(x^2+5\right)\)
Cách 2 dễ hơn nè !!
\(x^4+4x^2-5\)
\(=x^4-x^2+5x^2-5\)
\(=x^2\left(x^2-1\right)+5\left(x^2-1\right)\)
\(=\left(x^2-1\right)\left(x^2+5\right)\)
\(=\left(x-1\right)\left(x+1\right)\left(x^2+5\right)\)
