50.265 square mm
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A circle with a diameter of 4 mm has an area of : 12.57 mm2
When you try to figure out an area of a circle, you square the radius, then multiply it by pi to get the area of a circle. A radius square is radius x radius, or radius squared.
The area of any circle is (pi) x (radius)2 .The area of half the circle is just half of that number.
A circle with a radius of 2.5 meters has an area of 19.63 square meters.
A circle with a radius of 5 units has an area of 78.54 square units.