Geometry and Trigonometry

Measurements and Transformations

What are the measurements of a circle?

There are many measurements of a circle. The perimeter of a circle is actually called the circumference; to calculate this, multiply pi (π) times the diameter, dd), or pi (π) times twice the radius, r (2πr). The area of a circle is calculated by multiplying pi (π) times the radius squared, or πr2.


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