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 = 8} $.
$$ a \cdot c = 40 $$Step 3: Find out two numbers that multiply to $ a \cdot c = 40 $ and add to $ b = -14 $.
Step 4: All pairs of numbers with a product of $ 40 $ are:
PRODUCT = 40 | |
1 40 | -1 -40 |
2 20 | -2 -20 |
4 10 | -4 -10 |
5 8 | -5 -8 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = -14 }$
PRODUCT = 40 and SUM = -14 | |
1 40 | -1 -40 |
2 20 | -2 -20 |
4 10 | -4 -10 |
5 8 | -5 -8 |
Step 6: Replace middle term $ -14 x $ with $ -4x-10x $:
$$ 5x^{2}-14x+8 = 5x^{2}-4x-10x+8 $$Step 7: Apply factoring by grouping. Factor $ x $ out of the first two terms and $ -2 $ out of the last two terms.
$$ 5x^{2}-4x-10x+8 = x\left(5x-4\right) -2\left(5x-4\right) = \left(x-2\right) \left(5x-4\right) $$