Mới lên lớp 8 hả Ngô Tấn Đạt
Cách 1:
Ta có: \(x^2-x-12=x^2-x-16+4\)
\(=\left(x^2-16\right)-\left(x-4\right)\)
\(=\left(x-4\right)\left(x+4\right)-\left(x-4\right)\)
\(=\left(x-4\right)\left(x+4-1\right)\)
\(=\left(x-4\right)\left(x+3\right)\)
Cách 2:
\(x^2-x-12=x^2-x-9-3\)
\(=\left(x^2-9\right)-\left(x+3\right)\)
\(=\left(x-3\right)\left(x+3\right)-\left(x+3\right)\)
\(=\left(x+3\right)\left(x-4\right)\)
Cách 3:
\(x^2-x-12=x^2-4x+3x-12\)
\(=\left(x^2-4x\right)+\left(3x-12\right)\)
\(=x\left(x-4\right)+3\left(x-4\right)\)
\(=\left(x-4\right)\left(x+3\right)\)
Hok tốt!
