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