Step 1 :
After factoring out $ 3 $ we have:
$$ 30a^{2}-57a+18 = 3 ( 10a^{2}-19a+6 ) $$Step 2 :
Step 2: 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 3: Multiply the leading coefficient $\color{blue}{ a = 10 }$ by the constant term $\color{blue}{c = 6} $.
$$ a \cdot c = 60 $$Step 4: Find out two numbers that multiply to $ a \cdot c = 60 $ and add to $ b = -19 $.
Step 5: All pairs of numbers with a product of $ 60 $ are:
PRODUCT = 60 | |
1 60 | -1 -60 |
2 30 | -2 -30 |
3 20 | -3 -20 |
4 15 | -4 -15 |
5 12 | -5 -12 |
6 10 | -6 -10 |
Step 6: Find out which factor pair sums up to $\color{blue}{ b = -19 }$
PRODUCT = 60 and SUM = -19 | |
1 60 | -1 -60 |
2 30 | -2 -30 |
3 20 | -3 -20 |
4 15 | -4 -15 |
5 12 | -5 -12 |
6 10 | -6 -10 |
Step 7: Replace middle term $ -19 x $ with $ -4x-15x $:
$$ 10x^{2}-19x+6 = 10x^{2}-4x-15x+6 $$Step 8: Apply factoring by grouping. Factor $ 2x $ out of the first two terms and $ -3 $ out of the last two terms.
$$ 10x^{2}-4x-15x+6 = 2x\left(5x-2\right) -3\left(5x-2\right) = \left(2x-3\right) \left(5x-2\right) $$