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4. Find the approximate diameter of the
moon if an observer on the earth measures an angle of 0.50
from the top to the bottom of the disk when the moon is 240.000
km away.
Solution:
Let O be the eye of the observer. C is the centre
of the moon, r be the distance from O to C, and DE be a diameter
of the moon perpendicular to OC. Finally, Let A and B be the points
where the circle of radius r centered at O intersects the moon.
Then r is the approximate distance at O intersects the moon. Then
r is the approx. distance from the earth to the moon, and DE is
approx. S, where S = l (ACB).
Since r = 240,000 is probably accurate to only
two significant figures. Thus the most we can say is that the diameter
» 2100 km
5. Find the interior angles of a regular polygon of 10 sides
in radians.
Solution 
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