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