\(x^4-x^2-56\)
\(=x^4-8x^2+7x^2-56\)
\(=x^2\left(x^2-8\right)+7\left(x^2-8\right)\)
\(=\left(x^2-8\right)\left(x^2+7\right)\)
\(x^4-x^2-56=x^4+7x^2-8x^2-56=x^2\left(x^2+7\right)-8\left(x^2+7\right)\)
\(=\left(x^2+7\right)\left(x^2-8\right)\)
\(x^4-x^2-56\)
\(=x^4+7x^2-8x^2-56\)
\(=x^2\left(x^2+7\right)-8\left(x^2\:+7\right)\)
\(=\left(x^2+7\right)\left(x^2-8\right)\)
~ Rất vui vì giúp đc bn ~