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