\(8x^2-2\)
\(=2.\left(1^2-4x^2\right)\)
\(=2.\left(1-4x\right).\left(1+4x\right)\)
\(x^2-6x-y^2+9\)
\(=\left(x^2-6x+9\right)-y^2\)
\(=\left(x-3\right)^2-y^2\)
\(=\left(x-3-y\right).\left(x-3+y\right)\)
Mình sửa lại câu đầu ạ.
\(8x^2-2\)
\(=2.\left(4x^2-1\right)\)
\(=2.[\left(2x\right)^2-1^2]\)
\(=2.\left(2x-1\right).\left(2x+1\right)\)