Factor polynomial $$ 4x^{2}+3x-1 $$

$$ 4x^{2}+3x-1 = ( 4x-1 )( x+1 ) $$

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:

$$ a = 4 , b = 3 ~ \text{ and } ~ c = -1 $$

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 = 3 $.

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 $\color{blue}{ b = 3 }$

PRODUCT = -4 and SUM = 3
-1     4	1     -4
-2     2	2     -2

Step 6: Replace middle term $ 3 x $ with $ 4x-x $:

$$ 4x^{2}+3x-1 = 4x^{2}+4x-x-1 $$

Step 7: Apply factoring by grouping. Factor $ 4x $ out of the first two terms and $ -1 $ out of the last two terms.

$$ 4x^{2}+4x-x-1 = 4x\left(x+1\right) -1\left(x+1\right) = \left(4x-1\right) \left(x+1\right) $$

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