Factor polynomial $$ 5x^{2}+12x-9 $$

$$ 5x^{2}+12x-9 = ( 5x-3 )( x+3 ) $$

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:

$$ a = 5 , b = 12 ~ \text{ and } ~ c = -9 $$

Step 2: Multiply the leading coefficient $\color{blue}{ a = 5 }$ by the constant term $\color{blue}{c = -9} $.

$$ a \cdot c = -45 $$

Step 3: Find out two numbers that multiply to $ a \cdot c = -45 $ and add to $ b = 12 $.

Step 4: All pairs of numbers with a product of $ -45 $ are:

PRODUCT = -45
-1     45	1     -45
-3     15	3     -15
-5     9	5     -9

Step 5: Find out which factor pair sums up to $\color{blue}{ b = 12 }$

PRODUCT = -45 and SUM = 12
-1     45	1     -45
-3     15	3     -15
-5     9	5     -9

Step 6: Replace middle term $ 12 x $ with $ 15x-3x $:

$$ 5x^{2}+12x-9 = 5x^{2}+15x-3x-9 $$

Step 7: Apply factoring by grouping. Factor $ 5x $ out of the first two terms and $ -3 $ out of the last two terms.

$$ 5x^{2}+15x-3x-9 = 5x\left(x+3\right) -3\left(x+3\right) = \left(5x-3\right) \left(x+3\right) $$

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