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 $\color{blue}{ a = 2 }$ by the constant term $\color{blue}{c = -35} $.
$$ a \cdot c = -70 $$Step 3: Find out two numbers that multiply to $ a \cdot c = -70 $ and add to $ b = -3 $.
Step 4: All pairs of numbers with a product of $ -70 $ are:
PRODUCT = -70 | |
-1 70 | 1 -70 |
-2 35 | 2 -35 |
-5 14 | 5 -14 |
-7 10 | 7 -10 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = -3 }$
PRODUCT = -70 and SUM = -3 | |
-1 70 | 1 -70 |
-2 35 | 2 -35 |
-5 14 | 5 -14 |
-7 10 | 7 -10 |
Step 6: Replace middle term $ -3 x $ with $ 7x-10x $:
$$ 2x^{2}-3x-35 = 2x^{2}+7x-10x-35 $$Step 7: Apply factoring by grouping. Factor $ x $ out of the first two terms and $ -5 $ out of the last two terms.
$$ 2x^{2}+7x-10x-35 = x\left(2x+7\right) -5\left(2x+7\right) = \left(x-5\right) \left(2x+7\right) $$