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 $\color{blue}{ a = 9 }$ by the constant term $\color{blue}{c = -30} $.
$$ a \cdot c = -270 $$Step 3: Find out two numbers that multiply to $ a \cdot c = -270 $ and add to $ b = 49 $.
Step 4: All pairs of numbers with a product of $ -270 $ are:
PRODUCT = -270 | |
-1 270 | 1 -270 |
-2 135 | 2 -135 |
-3 90 | 3 -90 |
-5 54 | 5 -54 |
-6 45 | 6 -45 |
-9 30 | 9 -30 |
-10 27 | 10 -27 |
-15 18 | 15 -18 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = 49 }$
PRODUCT = -270 and SUM = 49 | |
-1 270 | 1 -270 |
-2 135 | 2 -135 |
-3 90 | 3 -90 |
-5 54 | 5 -54 |
-6 45 | 6 -45 |
-9 30 | 9 -30 |
-10 27 | 10 -27 |
-15 18 | 15 -18 |
Step 6: Replace middle term $ 49 x $ with $ 54x-5x $:
$$ 9x^{2}+49x-30 = 9x^{2}+54x-5x-30 $$Step 7: Apply factoring by grouping. Factor $ 9x $ out of the first two terms and $ -5 $ out of the last two terms.
$$ 9x^{2}+54x-5x-30 = 9x\left(x+6\right) -5\left(x+6\right) = \left(9x-5\right) \left(x+6\right) $$