Question

Phân tích đa thức sau thành nhân tử:

a) 3x²-30x+75

b) xy - x² - x + y 

c) x² -7x - 8

Answer 1

a,\(3x^2-30x+75=3\left(x^2-10x+25\right)=3\left(x-5\right)^2\)

b, \(xy-x^2-x+y=x\left(y-x\right)+\left(y-x\right)=\left(y-x\right)\left(x+1\right)\)

c,\(x^2-7x-8=x^2-8x+x-8=x\left(x-8\right)+\left(x-8\right)=\left(x-8\right)\left(x+1\right)\)

Answer 2

a) 3x² - 30x + 75 = 3.(x² - 10x + 25) = 3.(x² - 2.5.x + 5²) = 3.(x-5)²

b) xy - x² - x + y = x.(y-x) + (y-x) = (y-x).(x+1)

c) x² - 7x - 8 = x² + x - 8x - 8 = x.(x+1) - 8.(x+1) = (x+1).(x-8)