what is the rule for using diameter to find circumference?

If the diameter is 2* the length of the radius then d/2 then C=2pie+r.
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To find the circumference of a circle using the diameter, you can use the formula C = πd.

Here's how you can calculate it:
1. Start by determining the value of the diameter (d) of the circle.
2. Next, multiply the diameter by the mathematical constant pi (π), which is approximately 3.14159.
3. The result will be the circumference (C) of the circle.

So, the formula C = πd allows you to find the circumference of a circle by simply multiplying the diameter by pi.