the parameters in polar coordinates are r and thetaOriginally Posted byskippydurge

the parameters in rectangular coordinates are x and y

these are related be

x= r cos(theta)

y = r sin(theta)

x^2 + y^2 =r^2

your equation :r = cos [theta] + sin [theta]

multiply whole equation by r

r^2 = rcos [theta] + rsin [theta]

x^2 + y^2 = x +y