Step 1 :
After factoring out $ 3 $ we have:
$$ 15w^{2}+39w+18 = 3 ( 5w^{2}+13w+6 ) $$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 $\color{blue}{ a = 5 }$ by the constant term $\color{blue}{c = 6} $.
$$ a \cdot c = 30 $$Step 4: Find out two numbers that multiply to $ a \cdot c = 30 $ and add to $ b = 13 $.
Step 5: All pairs of numbers with a product of $ 30 $ are:
PRODUCT = 30 | |
1 30 | -1 -30 |
2 15 | -2 -15 |
3 10 | -3 -10 |
5 6 | -5 -6 |
Step 6: Find out which factor pair sums up to $\color{blue}{ b = 13 }$
PRODUCT = 30 and SUM = 13 | |
1 30 | -1 -30 |
2 15 | -2 -15 |
3 10 | -3 -10 |
5 6 | -5 -6 |
Step 7: Replace middle term $ 13 x $ with $ 10x+3x $:
$$ 5x^{2}+13x+6 = 5x^{2}+10x+3x+6 $$Step 8: Apply factoring by grouping. Factor $ 5x $ out of the first two terms and $ 3 $ out of the last two terms.
$$ 5x^{2}+10x+3x+6 = 5x\left(x+2\right) + 3\left(x+2\right) = \left(5x+3\right) \left(x+2\right) $$