Step 1: Identify constants $ a $ , $ b $ and $ c $.
$ a $ is a number in front of the $ x^2 $ term $ b $ is a number in front of the $ x $ term and $ c $ is a constant. In this case:
Step 2: Multiply the leading coefficient $\color{blue}{ a = 15 }$ by the constant term $\color{blue}{c = 6} $.
$$ a \cdot c = 90 $$Step 3: Find out two numbers that multiply to $ a \cdot c = 90 $ and add to $ b = -19 $.
Step 4: All pairs of numbers with a product of $ 90 $ are:
PRODUCT = 90 | |
1 90 | -1 -90 |
2 45 | -2 -45 |
3 30 | -3 -30 |
5 18 | -5 -18 |
6 15 | -6 -15 |
9 10 | -9 -10 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = -19 }$
PRODUCT = 90 and SUM = -19 | |
1 90 | -1 -90 |
2 45 | -2 -45 |
3 30 | -3 -30 |
5 18 | -5 -18 |
6 15 | -6 -15 |
9 10 | -9 -10 |
Step 6: Replace middle term $ -19 x $ with $ -9x-10x $:
$$ 15x^{2}-19x+6 = 15x^{2}-9x-10x+6 $$Step 7: Apply factoring by grouping. Factor $ 3x $ out of the first two terms and $ -2 $ out of the last two terms.
$$ 15x^{2}-9x-10x+6 = 3x\left(5x-3\right) -2\left(5x-3\right) = \left(3x-2\right) \left(5x-3\right) $$