Question

Factor completely: 18x2 − 21x − 15

3(2x + 1)(3x − 5)

3(2x − 5)(3x + 1)

3(2x − 1)(3x + 5)

3(6x + 1)(x − 5)

Answer 1

3(2x+1)(3x-5)

Answer 2

First, factor out the greatest common factor of all terms.
In this case it's 3, so you have
3(6x^2 - 7x - 5)
To factor the trinomial, multiply 6 and -5 to get -30.
Now you need to come up with two numbers that multiply to -30 and add to -7.
They are -10 and 3. Now break up the middle term into two terms with these numbers as coefficients: -7x = -10x + 3x. Rewrite the trinomial.
6x^2 - 10x + 3x - 5
Now factor a factor out of the first two terms of the trianomial and factor a factor out of the last two terms of the trinomial.
2x(3x - 5) + 1(3x - 5)
Now factor out the comon factor, 3x - 5:
(3x - 5)(2x + 1)
Now remember the 3 that we had already factored out:
18x^2 − 21x − 15 = 3(3x - 5)(2x + 1)
The last step is to look at every factor and see if it can be factored some more. In this case, no factor can be factored, so it's factored completely.