109.86=3.14*(r*r)

Solution for 109.86=3.14*(r*r) equation:

Simplifying
109.86 = 3.14(r * r)

Multiply r * r
109.86 = 3.14(r2)

Solving
109.86 = 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.
109.86 + -3.14r2 = 3.14r2 + -3.14r2

Combine like terms: 3.14r2 + -3.14r2 = 0.00
109.86 + -3.14r2 = 0.00

Add '-109.86' to each side of the equation.
109.86 + -109.86 + -3.14r2 = 0.00 + -109.86

Combine like terms: 109.86 + -109.86 = 0.00
0.00 + -3.14r2 = 0.00 + -109.86
-3.14r2 = 0.00 + -109.86

Combine like terms: 0.00 + -109.86 = -109.86
-3.14r2 = -109.86

Divide each side by '-3.14'.
r2 = 34.98726115

Simplifying
r2 = 34.98726115

Take the square root of each side:
r = {-5.915003056, 5.915003056}