There are two ways to do this:
Plot the points and connect them with a line segment:
Then we draw in these two line segments forming a right
triangle:
We count how many units long the bottom (horizontal) side of
that right triangle is and see that it is 9 units long. Then
we see that the left (vertical) side of the right triangle
is only 1 unit long. And the hypotenuse is the distance
between the desired points.
So we use the Pythagorean
theorem
Another way is to memorize the formula
and plug in , , ,
Either way we get the same answer.
The distance is
Edwin