To find distance between points $ A(x_1,y_1)$ and $ B(x_2,y_2)$, we use formula:

$$ \color{blue}{ d(A,B) = \sqrt{(x_2 - x_1)^2+(y_2 - y_1)^2} } $$

In this example we have:

$$ \begin{aligned} & A \left(7,~6\right) \implies x_1 = 7 ~~\text{and}~~ y_1 = 6 \\[1 em] & B \left(-2,~6\right) \implies x_2 = -2 ~~\text{and}~~ y_2 = 6 \end{aligned} $$

Substituting $ x_1 $, $ x_2 $, $ y_1 $ and $ y_2 $ into the formula above yields:

$$ \begin{aligned} d(A,B) & = \sqrt{\left( -2 - 7 \right)^2 + \left( 6 - 6 \right)^2} \\[1 em] d(A,B) & = \sqrt{ (-9)^2 + 0^2 } \\[1 em] d(A,B) & = \sqrt{ 81 + 0 } \\[1 em] d(A,B) & = \sqrt{ 81 } \\[1 em] d(A,B) & = 9 \end{aligned} $$

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