40478.78=4*3.14*r^2

Solution for 40478.78=4*3.14*r^2 equation:

Simplifying
40478.78 = 4 * 3.14r2

Multiply 4 * 3.14
40478.78 = 12.56r2

Solving
40478.78 = 12.56r2

Solving for variable 'r'.

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

Add '-12.56r2' to each side of the equation.
40478.78 + -12.56r2 = 12.56r2 + -12.56r2

Combine like terms: 12.56r2 + -12.56r2 = 0.00
40478.78 + -12.56r2 = 0.00

Add '-40478.78' to each side of the equation.
40478.78 + -40478.78 + -12.56r2 = 0.00 + -40478.78

Combine like terms: 40478.78 + -40478.78 = 0.00
0.00 + -12.56r2 = 0.00 + -40478.78
-12.56r2 = 0.00 + -40478.78

Combine like terms: 0.00 + -40478.78 = -40478.78
-12.56r2 = -40478.78

Divide each side by '-12.56'.
r2 = 3222.832803

Simplifying
r2 = 3222.832803

Take the square root of each side:
r = {-56.769999146, 56.769999146}