Step 1: 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 2: Multiply the leading coefficient $\color{blue}{ a = 5 }$ by the constant term $\color{blue}{c = -15} $.
$$ a \cdot c = -75 $$Step 3: Find out two numbers that multiply to $ a \cdot c = -75 $ and add to $ b = 22 $.
Step 4: All pairs of numbers with a product of $ -75 $ are:
PRODUCT = -75 | |
-1 75 | 1 -75 |
-3 25 | 3 -25 |
-5 15 | 5 -15 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = 22 }$
PRODUCT = -75 and SUM = 22 | |
-1 75 | 1 -75 |
-3 25 | 3 -25 |
-5 15 | 5 -15 |
Step 6: Replace middle term $ 22 x $ with $ 25x-3x $:
$$ 5x^{2}+22x-15 = 5x^{2}+25x-3x-15 $$Step 7: Apply factoring by grouping. Factor $ 5x $ out of the first two terms and $ -3 $ out of the last two terms.
$$ 5x^{2}+25x-3x-15 = 5x\left(x+5\right) -3\left(x+5\right) = \left(5x-3\right) \left(x+5\right) $$