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 = -14} $.
$$ a \cdot c = -42 $$Step 3: Find out two numbers that multiply to $ a \cdot c = -42 $ and add to $ b = -19 $.
Step 4: All pairs of numbers with a product of $ -42 $ are:
PRODUCT = -42 | |
-1 42 | 1 -42 |
-2 21 | 2 -21 |
-3 14 | 3 -14 |
-6 7 | 6 -7 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = -19 }$
PRODUCT = -42 and SUM = -19 | |
-1 42 | 1 -42 |
-2 21 | 2 -21 |
-3 14 | 3 -14 |
-6 7 | 6 -7 |
Step 6: Replace middle term $ -19 x $ with $ 2x-21x $:
$$ 3x^{2}-19x-14 = 3x^{2}+2x-21x-14 $$Step 7: Apply factoring by grouping. Factor $ x $ out of the first two terms and $ -7 $ out of the last two terms.
$$ 3x^{2}+2x-21x-14 = x\left(3x+2\right) -7\left(3x+2\right) = \left(x-7\right) \left(3x+2\right) $$