Trig
posted by Pam .
There is an airplane at an altitude of 12000 ft. The angle of depression is 1 degree. How far on the ground is the plane.

Did you make a sketch?
if so , you will see that
tan 1° = 12000/x , where x is the distance along the ground
x = 12000/tan 1° = .....
"How far on the ground is the plane ? " sounds like a very strange question.