Given that the plane is at altitude of 1200m and the angle of depression is 28°, to calculate the distance between the the plane and the rock we assume that we a have right triangle whereby the distance of the plane form the ground is the height, the distance from plane to the rock is the hypotenuse and the remaining distance is the base:
thus
sin θ=opposite/hypotenuse
θ=28°
opposite=1200m
hypotenuse=h
thus
sin 28=1200/h
h=1200/sin 28
h=2556.065 m
