The point that divides the segment into the ratio a:b is the weighted average of the endpoints, with the weights being "b" and "a". The weight of the first end point corresponds to the length of the far end of the segment.
Lets say pi is 3.14 The area of a circle is: pi*radius squared The radius is half the diameter so it is 5 inches. 3.14*5 squared 2 3.14*25 78.5inches squared