Step 1 :
After factoring out $ 2 $ we have:
$$ 4x^{2}+38x+70 = 2 ( 2x^{2}+19x+35 ) $$Step 2 :
Step 2: 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 3: Multiply the leading coefficient $\color{blue}{ a = 2 }$ by the constant term $\color{blue}{c = 35} $.
$$ a \cdot c = 70 $$Step 4: Find out two numbers that multiply to $ a \cdot c = 70 $ and add to $ b = 19 $.
Step 5: 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 6: Find out which factor pair sums up to $\color{blue}{ b = 19 }$
PRODUCT = 70 and SUM = 19 | |
1 70 | -1 -70 |
2 35 | -2 -35 |
5 14 | -5 -14 |
7 10 | -7 -10 |
Step 7: Replace middle term $ 19 x $ with $ 14x+5x $:
$$ 2x^{2}+19x+35 = 2x^{2}+14x+5x+35 $$Step 8: Apply factoring by grouping. Factor $ 2x $ out of the first two terms and $ 5 $ out of the last two terms.
$$ 2x^{2}+14x+5x+35 = 2x\left(x+7\right) + 5\left(x+7\right) = \left(2x+5\right) \left(x+7\right) $$