How do I factor these problems

x^3-2x^2-4x-8

x^7y^2-4x^5yy^2-21x^3y^2

]How do I factor these problems

x^3-2x^2-4x-8

This one is not easily factorable. It has 2 complex roots.

Are you sure you don't mean x^{3}-2x^{2}-4x+8

Otherwise, as you have it, the factorization is(which I pumped out with Maple):

(x+\frac{14403}{17161}+\frac{23073}{19028}I)\left( x+\frac{14403}{17161}-\frac{23073}{19028}I\right)(x-\frac{63025}{17133})


x^7y^2-4x^5yy^2-21x^3y^2

Is this what you mean:

x^{7}y^{2}-4x^{5}y^{2}-21x^{3}y^{2}?

The y I have highlighted. I suppose it's errant?

If this is correct, then factor out x^{3} \;\ and \;\ y^{2}:

x^{3}y^{2}(x^{4}-4x^{2}-21)

Factor in the parentheses by letting u=x^{2}

(u^{2}-4u-21)=(u-7)(u+3)

Resub:

x^{3}y^{2}(x^{2}-7)(x^{2}+3)

If you mean x^3 - 2x^2 - 4x + 8, then this equals
x^2(x-2) - 4(x-2) = (x^2 - 4) (x-2) = (x+2)(x-2)^2