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 $\color{blue}{ a = 6 }$ by the constant term $\color{blue}{c = -13} $.
$$ a \cdot c = -78 $$Step 3: Find out two numbers that multiply to $ a \cdot c = -78 $ and add to $ b = -7 $.
Step 4: All pairs of numbers with a product of $ -78 $ are:
PRODUCT = -78 | |
-1 78 | 1 -78 |
-2 39 | 2 -39 |
-3 26 | 3 -26 |
-6 13 | 6 -13 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = -7 }$
PRODUCT = -78 and SUM = -7 | |
-1 78 | 1 -78 |
-2 39 | 2 -39 |
-3 26 | 3 -26 |
-6 13 | 6 -13 |
Step 6: Replace middle term $ -7 x $ with $ 6x-13x $:
$$ 6x^{2}-7x-13 = 6x^{2}+6x-13x-13 $$Step 7: Apply factoring by grouping. Factor $ 6x $ out of the first two terms and $ -13 $ out of the last two terms.
$$ 6x^{2}+6x-13x-13 = 6x\left(x+1\right) -13\left(x+1\right) = \left(6x-13\right) \left(x+1\right) $$