If the angular diameter of the moon be 30, how far from the eye a coin of diameter `2. 2c m` be kept to hide the moon?

Explanation

To solve the problem, we need to find the distance at which a coin of diameter 2.2 cm must be placed in order to hide the moon, given that the angular diameter of the moon is 30 minutes.

### Step-by-Step Solution:

1. **Convert Angular Diameter to Radians**:
The angular diameter of the moon is given as 30 minutes. First, we need to convert this into degrees and then into radians.
\[
30 \text{ minutes} = \frac{30}{60} \text{ degrees} = 0.5 \text{ degrees}
...