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 $\color{blue}{ a = 8 }$ by the constant term $\color{blue}{c = 63} $.
$$ a \cdot c = 504 $$Step 3: Find out two numbers that multiply to $ a \cdot c = 504 $ and add to $ b = -50 $.
Step 4: All pairs of numbers with a product of $ 504 $ are:
PRODUCT = 504 | |
1 504 | -1 -504 |
2 252 | -2 -252 |
3 168 | -3 -168 |
4 126 | -4 -126 |
6 84 | -6 -84 |
7 72 | -7 -72 |
8 63 | -8 -63 |
9 56 | -9 -56 |
12 42 | -12 -42 |
14 36 | -14 -36 |
18 28 | -18 -28 |
21 24 | -21 -24 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = -50 }$
PRODUCT = 504 and SUM = -50 | |
1 504 | -1 -504 |
2 252 | -2 -252 |
3 168 | -3 -168 |
4 126 | -4 -126 |
6 84 | -6 -84 |
7 72 | -7 -72 |
8 63 | -8 -63 |
9 56 | -9 -56 |
12 42 | -12 -42 |
14 36 | -14 -36 |
18 28 | -18 -28 |
21 24 | -21 -24 |
Step 6: Replace middle term $ -50 x $ with $ -14x-36x $:
$$ 8x^{2}-50x+63 = 8x^{2}-14x-36x+63 $$Step 7: Apply factoring by grouping. Factor $ 2x $ out of the first two terms and $ -9 $ out of the last two terms.
$$ 8x^{2}-14x-36x+63 = 2x\left(4x-7\right) -9\left(4x-7\right) = \left(2x-9\right) \left(4x-7\right) $$