Step 1 :
After factoring out $ 6 $ we have:
$$ 42p^{2}+456p+360 = 6 ( 7p^{2}+76p+60 ) $$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 $\color{blue}{ a = 7 }$ by the constant term $\color{blue}{c = 60} $.
$$ a \cdot c = 420 $$Step 4: Find out two numbers that multiply to $ a \cdot c = 420 $ and add to $ b = 76 $.
Step 5: All pairs of numbers with a product of $ 420 $ are:
PRODUCT = 420 | |
1 420 | -1 -420 |
2 210 | -2 -210 |
3 140 | -3 -140 |
4 105 | -4 -105 |
5 84 | -5 -84 |
6 70 | -6 -70 |
7 60 | -7 -60 |
10 42 | -10 -42 |
12 35 | -12 -35 |
14 30 | -14 -30 |
15 28 | -15 -28 |
20 21 | -20 -21 |
Step 6: Find out which factor pair sums up to $\color{blue}{ b = 76 }$
PRODUCT = 420 and SUM = 76 | |
1 420 | -1 -420 |
2 210 | -2 -210 |
3 140 | -3 -140 |
4 105 | -4 -105 |
5 84 | -5 -84 |
6 70 | -6 -70 |
7 60 | -7 -60 |
10 42 | -10 -42 |
12 35 | -12 -35 |
14 30 | -14 -30 |
15 28 | -15 -28 |
20 21 | -20 -21 |
Step 7: Replace middle term $ 76 x $ with $ 70x+6x $:
$$ 7x^{2}+76x+60 = 7x^{2}+70x+6x+60 $$Step 8: Apply factoring by grouping. Factor $ 7x $ out of the first two terms and $ 6 $ out of the last two terms.
$$ 7x^{2}+70x+6x+60 = 7x\left(x+10\right) + 6\left(x+10\right) = \left(7x+6\right) \left(x+10\right) $$