Answer: 7 units
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Short explanation:
Plot the points (3,1) and (3,8). Note how they line up vertically. Count the number of vertical spaces between them and you should get 7 units. This only works if the points line up horizontally or vertically.
Or you could subtract the y coordinates to get 8-1 = 7, which is an alternative to graphing and counting the spaces. This is preferred if there is a very large gap.
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Longer method:
Use the distance formula with (x1,y1) = (3,1) and (x2,y2) = (3,8)
[tex]d = \sqrt{(x_1 - x_2)^2 + (y_1 - y_2)^2}\\\\d = \sqrt{(3-3)^2 + (1-8)^2}\\\\d = \sqrt{(0)^2 + (-7)^2}\\\\d = \sqrt{0 + 49}\\\\d = \sqrt{49}\\\\d = 7\\\\[/tex]
