4x21
x2 - 4
Answer: x (x2-x)
x2-3x-28
4*21=84.
4x21
x2 - 4
9 - x2 will factor into (3 - x)(3 + x)
Answer: x (x2-x)
x2-3x-28
x2-14 does factor but not pretty; it factors to: (x+sqrt14)(x-sqrt14).
4*21=84.
x2-x=x(x-1)
x2 + 6x - 2 can not be factored
x2(x3 + 1) is the best you can do there.
x2-9x = x(x-9)
x2 - 13 + 30 = x2 + 17, which has no real factors.