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 $\color{blue}{ a = 12 }$ by the constant term $\color{blue}{c = -12} $.
$$ a \cdot c = -144 $$Step 3: Find out two numbers that multiply to $ a \cdot c = -144 $ and add to $ b = -143 $.
Step 4: All pairs of numbers with a product of $ -144 $ are:
PRODUCT = -144 | |
-1 144 | 1 -144 |
-2 72 | 2 -72 |
-3 48 | 3 -48 |
-4 36 | 4 -36 |
-6 24 | 6 -24 |
-8 18 | 8 -18 |
-9 16 | 9 -16 |
-12 12 | 12 -12 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = -143 }$
PRODUCT = -144 and SUM = -143 | |
-1 144 | 1 -144 |
-2 72 | 2 -72 |
-3 48 | 3 -48 |
-4 36 | 4 -36 |
-6 24 | 6 -24 |
-8 18 | 8 -18 |
-9 16 | 9 -16 |
-12 12 | 12 -12 |
Step 6: Replace middle term $ -143 x $ with $ x-144x $:
$$ 12x^{2}-143x-12 = 12x^{2}+x-144x-12 $$Step 7: Apply factoring by grouping. Factor $ x $ out of the first two terms and $ -12 $ out of the last two terms.
$$ 12x^{2}+x-144x-12 = x\left(12x+1\right) -12\left(12x+1\right) = \left(x-12\right) \left(12x+1\right) $$