Question

k ) \(x^2-9\)

Answer 1

\(x^2-9=x^2-3^2=\left(x+3\right)\left(x-3\right)\)

Answer 2

\(x^2-9\)

\(=x^2-3^2\)

\(=\left(x+3\right).\left(x-3\right)\)

Answer 3

\(x^2-3^2=\left(x+3\right)\left(x-3\right)\)(hằng đẳng thức số 3)

Answer 4

\(x^2-9=x^2-3^2=\left(x+3\right)\left(x-3\right)\)