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