Introductory Algebra for College Students (7th Edition)

d=$\frac{C}{\pi}$
C=$\pi$d $\pi$d=C $\frac{\pi d}{\pi}$=$\frac{C}{\pi}$ d=$\frac{C}{\pi}$ The given is the circumference formula which means that circumference is equal to the product of 2, pi, and the radius.