Answer
a. $ 2x(x-5)$.
b. $ (x+3)(x-2)(x+2)$
Work Step by Step
We have
a. Factoring $2x$ out we get: $$2x^2 - 10x=2x(x-5)$$
b. We factor by grouping, so first we group the first two terms together and the last two terms together:
$$=(x^3 + 3x^2)+(- 4x - 12)$$
Then we factor out the GCF in each group:
$$=x^2(x+3)-4(x+3)$$.
Then we factor out $x+3$ out we have
$$=(x+3)(x^2-4) $$
Finally we factor $(x^2-4)$ as a difference of two squares to obtain:
$$=(x+3)(x-2)(x+2)$$
