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 $\color{blue}{ a = 10 }$ by the constant term $\color{blue}{c = -7} $.
$$ a \cdot c = -70 $$Step 3: Find out two numbers that multiply to $ a \cdot c = -70 $ and add to $ b = 33 $.
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 $\color{blue}{ b = 33 }$
PRODUCT = -70 and SUM = 33 | |
-1 70 | 1 -70 |
-2 35 | 2 -35 |
-5 14 | 5 -14 |
-7 10 | 7 -10 |
Step 6: Replace middle term $ 33 x $ with $ 35x-2x $:
$$ 10x^{2}+33x-7 = 10x^{2}+35x-2x-7 $$Step 7: Apply factoring by grouping. Factor $ 5x $ out of the first two terms and $ -1 $ out of the last two terms.
$$ 10x^{2}+35x-2x-7 = 5x\left(2x+7\right) -1\left(2x+7\right) = \left(5x-1\right) \left(2x+7\right) $$