Question

Identify the factors of 3a2 + 28a − 20.

(3a − 4)(a + 5)

(3a + 4)(a − 5)

(3a + 2)(a − 10)

(3a − 2)(a + 10)

Answer 1

3a^2 + 28a - 20

First multiply 3 by -20 giving you -60 and then find the factors of -60:
1 * -60
2 * -30
3 * -20
4 * -15
5 * -12
6 * -10
Pick the two numbers that add up to 28. So we have 2 and -30. Now what we do is kinda split 28a in half.

3a^2 + 2a -30a - 20

Now move them around so it becomes convenient to factor.

(3a^2 - 30a) (2a - 20)

Find the GCF for both of them so for the first one you have 3a and for the second one you have 2 and then you put what number or variable you would need in order to solve it back into the original form:

3a(a - 10) and 2(a - 10)

Now you get the two GCF's and put them inside parenthesis while the identical ones go in another pair of parenthesis:

(a - 10) and (3a + 2)