If an airplane flies 100 miles due north, then turns and flies 100 miles directly northeast, how far is it the?

This is probably a math homework (geometry) question, which I won't do for you. But because it mentions flying an airplane, it is important to use the following skill, which will be useful for the rest of your life: State your assumptions before solving the problem. Here, state your assumptions concerning airplane altitude throughout the flight, curvature of the Earth and anything else that comes to mind.