You cannot calculate pi with a radius, but pi as a constant is 3.14159265358979323846, and continues on as an irrational number. If you are trying to calculate the area of a circle, the formula is pi X R squared. If R = 5, the the are is 25 X pi.<br><p></p><p>
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A=pi times R squared If the radius is 5, the area is 25pi
The area of a circle of radius r is pi*r*r
A radius is not part of pi.
The circumference of a circle that has a radius of 5 inches is 10 X pi or approximatly 31.415926535897932384626433832795. If you know the radius you can find the circumference by multiplying it by 2(pi)
Circumference / pi = Diameter, radius = diameter / 2 So> 37 / pi = 11.777 diameter = 5.8885 radius * * * * * If you wish to give your answer to 5 significant figures, you MUST use the value of pi to at least that many sig figs. Thus, radius = 37/(2*3.1416) = 5.8887 - to 5 sig figs.