Question

https://clackamasweb.owschools.com/media/g_geo_ccss_2014/10/q5l1gra.gif

What is the length of AA' ?

Answer 1

@SolomonZelman

Answer 2

If you draw a line from A to A', you'll see that you get a right triangle. I have edited your image to reflect that.
You can then relate the sides by use of the Pythagorean theorem:
\[a^2 + b^2 = c^2\]

Answer 3

Or you can find the distance from one point to the other with the distance formula.