\(x^4+81\)
\(=x^4+3^4\)
\(=\left(x^2+3^2\right)^2-2x^23^2\)
\(=\left(x^2+\sqrt{2}x3+3^2\right)\left(x^2-\sqrt{2}x3+3^2\right)\)
nguồn gg
\(x^4+81\)
\(=x^4+18x^2+81-18x^2\)
\(=\left(x^2+9\right)^2-18x^2\)
\(=\left(x^2-3\sqrt{2}x+9\right)\left(x^2+3\sqrt{2}x+9\right)\)