Câu 1:
a: \(=\left(x-1\right)\left(x-5\right)\)
b: \(=2x^2-8x+3x-12=\left(x-4\right)\left(2x+3\right)\)
c: \(=\left(x-4\right)\left(x+3\right)\)
d: =(x-4)(x-9)
e: \(=\left(x+3\right)\left(x+5\right)\)
f: \(=3x^2-15x-x+5=\left(x-5\right)\left(3x-1\right)\)