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