78=3.1416*R^2

Solution for 78=3.1416*R^2 equation:

Simplifying
78 = 3.1416R2

Solving
78 = 3.1416R2

Solving for variable 'R'.

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

Add '-3.1416R2' to each side of the equation.
78 + -3.1416R2 = 3.1416R2 + -3.1416R2

Combine like terms: 3.1416R2 + -3.1416R2 = 0.0000
78 + -3.1416R2 = 0.0000

Add '-78' to each side of the equation.
78 + -78 + -3.1416R2 = 0.0000 + -78

Combine like terms: 78 + -78 = 0
0 + -3.1416R2 = 0.0000 + -78
-3.1416R2 = 0.0000 + -78

Combine like terms: 0.0000 + -78 = -78
-3.1416R2 = -78

Divide each side by '-3.1416'.
R2 = 24.82811306

Simplifying
R2 = 24.82811306

Take the square root of each side:
R = {-4.982781659, 4.982781659}