Answer:
You would either need to complete the square, use the quadratic equation, or another method because when reduced by the common factor, the constant term c is prime which means that it is only divisible by one and itself. Because the possible rational factors determined by c do not add up to the b term, it cannot be factored.
Step-by-step explanation:
3x² + 24x - 15 = 0
3(x² + 8x - 5) = 0
[find the greatest common factor between each term and move the coefficient outside of the expression; in this case it's 3 since 3 fits into numbers 3, 24, and -15 so that it cannot be reduced further]
Then you can either use the box or pq method (since a is 1) to find working factors.
x² + bx + c → (x + p)(x + q).
p + q = b.
pq = c.
In this case with 3(x² + 8x - 5), b is 8 and c is -5.
This means we need two numbers that add up to 8 and multiply to -5.
Since -5 is prime, our only options are ±1 for p and ∓5 for q. This is because these are the only factors which multiply to -5.
1 + -5 = -4 ≠ 8
-1 + 5 = 4 ≠ 8.
Since we cannot find rational solutions, this cannot be factored, and so we must use another method.