To solve the equation square root of (20 - r) = r, square both sides to form a quadratic equation, factor it, and consider only the non-negative solution, which gives r = 4.
The equation given is square root of (20 - r) = r. To solve for r, we first need to square both sides to get rid of the square root, resulting in 20 - r = r². Rearrange and combine like terms to get the quadratic equation r² + r - 20 = 0.
Use the quadratic formula or factoring to find the values of r. In this case, the equation can be factored as (r + 5)(r - 4) = 0, which gives us r = -5 or r = 4.
However, because we initially took a square root, we must consider only the non-negative solution, so r = 4 is the suitable answer.