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 = 24} $.
$$ a \cdot c = 120 $$Step 3: Find out two numbers that multiply to $ a \cdot c = 120 $ and add to $ b = -43 $.
Step 4: All pairs of numbers with a product of $ 120 $ are:
PRODUCT = 120 | |
1 120 | -1 -120 |
2 60 | -2 -60 |
3 40 | -3 -40 |
4 30 | -4 -30 |
5 24 | -5 -24 |
6 20 | -6 -20 |
8 15 | -8 -15 |
10 12 | -10 -12 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = -43 }$
PRODUCT = 120 and SUM = -43 | |
1 120 | -1 -120 |
2 60 | -2 -60 |
3 40 | -3 -40 |
4 30 | -4 -30 |
5 24 | -5 -24 |
6 20 | -6 -20 |
8 15 | -8 -15 |
10 12 | -10 -12 |
Step 6: Replace middle term $ -43 x $ with $ -3x-40x $:
$$ 5x^{2}-43x+24 = 5x^{2}-3x-40x+24 $$Step 7: Apply factoring by grouping. Factor $ x $ out of the first two terms and $ -8 $ out of the last two terms.
$$ 5x^{2}-3x-40x+24 = x\left(5x-3\right) -8\left(5x-3\right) = \left(x-8\right) \left(5x-3\right) $$