The equation c = πd + 9 is a formula from mathematics used to find the circumference of a circle given its diameter.
This equation is not from physics, but rather from mathematics. It is a formula for finding the circumference of a circle given its diameter. The equation is:
c = πd + 9
Where 'c' represents the circumference of the circle and 'd' represents its diameter. The value '9' seems to be an additional constant added to the formula. So if you know the value of 'd', you can substitute it into the equation to find the circumference 'c'.