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 $\color{blue}{ a = 24 }$ by the constant term $\color{blue}{c = 49} $.
$$ a \cdot c = 1176 $$Step 3: Find out two numbers that multiply to $ a \cdot c = 1176 $ and add to $ b = 70 $.
Step 4: All pairs of numbers with a product of $ 1176 $ are:
PRODUCT = 1176 | |
1 1176 | -1 -1176 |
2 588 | -2 -588 |
3 392 | -3 -392 |
4 294 | -4 -294 |
6 196 | -6 -196 |
7 168 | -7 -168 |
8 147 | -8 -147 |
12 98 | -12 -98 |
14 84 | -14 -84 |
21 56 | -21 -56 |
24 49 | -24 -49 |
28 42 | -28 -42 |
Step 5: Find out which factor pair sums up to $\color{blue}{ b = 70 }$
PRODUCT = 1176 and SUM = 70 | |
1 1176 | -1 -1176 |
2 588 | -2 -588 |
3 392 | -3 -392 |
4 294 | -4 -294 |
6 196 | -6 -196 |
7 168 | -7 -168 |
8 147 | -8 -147 |
12 98 | -12 -98 |
14 84 | -14 -84 |
21 56 | -21 -56 |
24 49 | -24 -49 |
28 42 | -28 -42 |
Step 6: Replace middle term $ 70 x $ with $ 42x+28x $:
$$ 24x^{2}+70x+49 = 24x^{2}+42x+28x+49 $$Step 7: Apply factoring by grouping. Factor $ 6x $ out of the first two terms and $ 7 $ out of the last two terms.
$$ 24x^{2}+42x+28x+49 = 6x\left(4x+7\right) + 7\left(4x+7\right) = \left(6x+7\right) \left(4x+7\right) $$