Find an Equivalent Equation in Rectangular Coordinates $$r = \cos \theta$$

Multiple Choice

Find an equivalent equation in rectangular coordinates.
- $$r = \cos \theta$$

A) $( x + y ) ^ { 2 } = y$
B) $x ^ { 2 } + y ^ { 2 } = y$
C) $x ^ { 2 } + y ^ { 2 } = x$
D) $( x + y ) ^ { 2 } = x$