Consider a unit circle,

Then

In a circle (shown in the attached diagram) of unit radius the figure enclosed by the ordinates x = 0, y =1 and x = 1/2, is made up of a segment enclosing an angle of 30 (degrees) between its two radii, of area Pi/12, and of a triangle whose area 1/2xy = (sqrt 3)/8. So we can write:

or

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