Question

the letters r and represent polar coordinates. Write each equation using rectangular coordinates (x,y):
r=cosƟ

Answer 1

multiply both sides by r : r^2 = rcos(theta)
x^2 +y^2 = x
x^2 -x +1/4 +y^2 = 1/4 (add both sides by 1/4 to make it quadratic equation)
(x-1/2)^2 +y^2 = 1/4
this is circle center (1/2,0) radius 1/2