Find a polar equation that has the same graph as the equation in x and y.

x^2 + y^2 = 5

X^2 + y^2 can be replaced by r^2 to obtain the polar equation equivalent to x^2 + y^2 = 5. Thus, r^2 = 5, and r = sqrt (5). That's all that's necessary. No matter what the angle is, r will always be sqrt (5).