While landing at an airport, a pilot made an angle of depression of 20°.

Let’s denote the height at which the plane was when it started landing by h (in meters).

We know that the angle of depression of 20° is formed between the horizontal ground and the line of sight from the plane to the point on the ground directly below it. This means that the angle of elevation from the point on the ground directly below the plane to the plane itself is also 20°.

Using trigonometry, we can find that the horizontal distance covered by the plane during the 54 seconds of landing is:

d = v × t = 200 × (54/3600) = 3 km

Now, we can use the trigonometric tangent function to relate the height h to the distance d and the angle of elevation:

tan 20° = h / d

Solving for h, we get:

h = d × tan 20° = 3000 × 0.364 = 1092 meters

Therefore, the height at which the plane was when it started landing was approximately 1092 meters.