Step 1 :
After factoring out $ 2 $ we have:
$$ 36y^{2}+114y-20 = 2 ( 18y^{2}+57y-10 ) $$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 $\color{blue}{ a = 18 }$ by the constant term $\color{blue}{c = -10} $.
$$ a \cdot c = -180 $$Step 4: Find out two numbers that multiply to $ a \cdot c = -180 $ and add to $ b = 57 $.
Step 5: All pairs of numbers with a product of $ -180 $ are:
PRODUCT = -180 | |
-1 180 | 1 -180 |
-2 90 | 2 -90 |
-3 60 | 3 -60 |
-4 45 | 4 -45 |
-5 36 | 5 -36 |
-6 30 | 6 -30 |
-9 20 | 9 -20 |
-10 18 | 10 -18 |
-12 15 | 12 -15 |
Step 6: Find out which factor pair sums up to $\color{blue}{ b = 57 }$
PRODUCT = -180 and SUM = 57 | |
-1 180 | 1 -180 |
-2 90 | 2 -90 |
-3 60 | 3 -60 |
-4 45 | 4 -45 |
-5 36 | 5 -36 |
-6 30 | 6 -30 |
-9 20 | 9 -20 |
-10 18 | 10 -18 |
-12 15 | 12 -15 |
Step 7: Replace middle term $ 57 x $ with $ 60x-3x $:
$$ 18x^{2}+57x-10 = 18x^{2}+60x-3x-10 $$Step 8: Apply factoring by grouping. Factor $ 6x $ out of the first two terms and $ -1 $ out of the last two terms.
$$ 18x^{2}+60x-3x-10 = 6x\left(3x+10\right) -1\left(3x+10\right) = \left(6x-1\right) \left(3x+10\right) $$