Step 1: Identify constants $ \color{blue}{ b }$ and $\color{red}{ c }$. ( $ \color{blue}{ b }$ is a number in front of the $ x $ term and $ \color{red}{ c } $ is a constant). In our case:

$$ \color{blue}{ b = -14 } ~ \text{ and } ~ \color{red}{ c = 13 }$$

Now we must discover two numbers that sum up to $ \color{blue}{ -14 } $ and multiply to $ \color{red}{ 13 } $.

Step 2: Find out pairs of numbers with a product of $\color{red}{ c = 13 }$.

PRODUCT = 13
1     13	-1     -13

Step 3: Find out which pair sums up to $\color{blue}{ b = -14 }$

PRODUCT = 13 and SUM = -14
1     13	-1     -13

Step 4: Put -1 and -13 into placeholders to get factored form.

$$ \begin{aligned} d^{2}-14d+13 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ d^{2}-14d+13 & = (x -1)(x -13) \end{aligned} $$

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