The angle of elevation of a jet fighter from a point A on the ground is 60° . after a flight of 15 seconds the angle of elevation changes to 30° .if the jet is flying at the speed 720 km/h find the constant height at which the jet is flying.

The figure is given below:

Let jet fly at a constant height of y km

and let the distance from a point to the starting point of jet bet x km.

Thus, BD = EC = y km

And, AB = x km

As distance = speed × time.

Distance took by jet to travel from D to E =

DE = 3km

Using trigonometry;

∠ DAB = 60°

tan 60° = √3

Also,∠ EAC = 30°

y = 2.59 m

So, the constant height of the jet is 2.59 km