0=r^2-13.6900

Solution for 0=r^2-13.6900 equation:

Simplifying
0 = r2 + -13.6900

Reorder the terms:
0 = -13.6900 + r2

Solving
0 = -13.6900 + r2

Solving for variable 'r'.

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

Add '-1r2' to each side of the equation.
0 + -1r2 = -13.6900 + r2 + -1r2
Remove the zero:
-1r2 = -13.6900 + r2 + -1r2

Combine like terms: r2 + -1r2 = 0
-1r2 = -13.6900 + 0
-1r2 = -13.6900

Divide each side by '-1'.
r2 = 13.69

Simplifying
r2 = 13.69

Take the square root of each side:
r = {-3.7, 3.7}