thus, the whole circle's area is 100pi square units.
...and this shape is exactly one quarter, one-fourth, of the whole circle. <em>Why? because of the shape's right angle and radius. (when you multiply 90 times 4, it will equal 360 degrees, which is the angle of a whole circle.)</em>
so 100pi divided by 4 equals 25pi square units of the shape.
ANSWER:
25 pi square units
(or in decimals: multiply 25 by 3.14 which would be 78.5 square units)
