Question

ACT/SAT A passenger in a hot-air balloon spots a small fire on the ground. The angle of depression to the fire is 30°, and the height of the hot-air balloon is 150 feet. To the nearest foot, what is the horizontal distance from the hot-air balloon to the fire?

Answer 1

Explanation:

law of sine :

a/sin(A) = b/sin(B) = c/sin(C)

a,b,c being the sides of the triangle, A, B, C are the corresponding opposite angles in the triangle.

the angle of depression is the external angle of the triangle vertex at the balloon. that means the internal angle is 60°, as both together must be 90° (the angle between the height of the balloon and the horizontal line at the balloon).

the angles at the ground at the fire are mirrored : the internal angle there is 30°, the external angle is 60°.

and so,

height/sin(30) = 150/0.5 = distance/sin(60)

distance = sin(60)×150/0.5 = sin(60)×300 =

= 259.8076211... ft ≈ 260 ft