78.5=r^2*3.14

Solution for 78.5=r^2*3.14 equation:

Simplifying
78.5 = r2 * 3.14

Reorder the terms for easier multiplication:
78.5 = 3.14r2

Solving
78.5 = 3.14r2

Solving for variable 'r'.

Move all terms containing r to the left, all other terms to the right.

Add '-3.14r2' to each side of the equation.
78.5 + -3.14r2 = 3.14r2 + -3.14r2

Combine like terms: 3.14r2 + -3.14r2 = 0.00
78.5 + -3.14r2 = 0.00

Add '-78.5' to each side of the equation.
78.5 + -78.5 + -3.14r2 = 0.00 + -78.5

Combine like terms: 78.5 + -78.5 = 0.0
0.0 + -3.14r2 = 0.00 + -78.5
-3.14r2 = 0.00 + -78.5

Combine like terms: 0.00 + -78.5 = -78.5
-3.14r2 = -78.5

Divide each side by '-3.14'.
r2 = 25

Simplifying
r2 = 25

Take the square root of each side:
r = {-5, 5}