Step 1 :
After factoring out $ 6 $ we have:
$$ 18x^{2}+96x-72 = 6 ( 3x^{2}+16x-12 ) $$Step 2 :
Step 2: 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 3: Multiply the leading coefficient $\color{blue}{ a = 3 }$ by the constant term $\color{blue}{c = -12} $.
$$ a \cdot c = -36 $$Step 4: Find out two numbers that multiply to $ a \cdot c = -36 $ and add to $ b = 16 $.
Step 5: All pairs of numbers with a product of $ -36 $ are:
PRODUCT = -36 | |
-1 36 | 1 -36 |
-2 18 | 2 -18 |
-3 12 | 3 -12 |
-4 9 | 4 -9 |
-6 6 | 6 -6 |
Step 6: Find out which factor pair sums up to $\color{blue}{ b = 16 }$
PRODUCT = -36 and SUM = 16 | |
-1 36 | 1 -36 |
-2 18 | 2 -18 |
-3 12 | 3 -12 |
-4 9 | 4 -9 |
-6 6 | 6 -6 |
Step 7: Replace middle term $ 16 x $ with $ 18x-2x $:
$$ 3x^{2}+16x-12 = 3x^{2}+18x-2x-12 $$Step 8: Apply factoring by grouping. Factor $ 3x $ out of the first two terms and $ -2 $ out of the last two terms.
$$ 3x^{2}+18x-2x-12 = 3x\left(x+6\right) -2\left(x+6\right) = \left(3x-2\right) \left(x+6\right) $$