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 $\color{blue}{ a = 5 }$ by the constant term $\color{blue}{c = -6} $.
$$ a \cdot c = -30 $$Step 3: Find out two numbers that multiply to $ a \cdot c = -30 $ and add to $ b = 13 $.
Step 4: All pairs of numbers with a product of $ -30 $ are:
PRODUCT = -30 | |
-1 30 | 1 -30 |
-2 15 | 2 -15 |
-3 10 | 3 -10 |
-5 6 | 5 -6 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = 13 }$
PRODUCT = -30 and SUM = 13 | |
-1 30 | 1 -30 |
-2 15 | 2 -15 |
-3 10 | 3 -10 |
-5 6 | 5 -6 |
Step 6: Replace middle term $ 13 x $ with $ 15x-2x $:
$$ 5x^{2}+13x-6 = 5x^{2}+15x-2x-6 $$Step 7: Apply factoring by grouping. Factor $ 5x $ out of the first two terms and $ -2 $ out of the last two terms.
$$ 5x^{2}+15x-2x-6 = 5x\left(x+3\right) -2\left(x+3\right) = \left(5x-2\right) \left(x+3\right) $$