Answer:
[tex]\large\boxed{C=2\pi r}[/tex]
Step-by-step explanation:
A linear equation is an equation in which a variable is in the first power.
The formula of a Circumference of a circle
[tex]C=2\pi r\\\\2,\ \pi-\text{numbers}\\r-\text{variable}\\\\\boxed{\bold{YES}}[/tex]
The formula of an Area of a circle
[tex]A=\pi r^2\\\\\pi-\text{number}\\r^2-\text{variable in the second power}\\\\\boxed{\bold{NO}}[/tex]
The formula of a volume of a sphere
[tex]V=\dfrac{4}{3}\pi r^3\\\\\dfrac{4}{3},\ \pi-\text{numbers}\\r^3-\text{variable in the third power}\\\\\boxed{\bold{NO}}[/tex]
