Have you used the Pythagorean Theorem before? If not, make sure to check out the Pythagorean Theorem lesson. If you have, you already know how to find the distance between two points! We usually think of the Pythagorean Theorem only for a right triangle that's drawn, but you can also use it to find the distance between two points on a plane.
Let's say you have to find the distance between the two points shown in the graph below. If we use the grid lines to draw in lines down and across, we can form a right triangle! Now that we have a right triangle, we can use the Pythagorean Theorem to find the distance between A and B. The distance we want to find is the hypotenuse of the right triangle and we can just count the spaces to find the lengths of the legs. Let's look at another example. Let's say you have to find the distance between the points (1,2) and (6,4). First, let's plot the points on a graph and draw in the line segment between the two points. We need to find the length of this segment. Next, we can use the grid lines to create a right triangle. The distance we want to find is the hypotenuse of the right triangle and we can just count the spaces down and over to find the lengths of the legs. We can plug these values into the Pythagorean Theorem and solve for x. 
