Question

Transform the following polar equation into an equation in rectangular coordinates: r=4

Answer 1

The answer is letter D. 
Solution:
r=4
r^2=4^2
r^2=16
r^2=x^2+y^2=16
x^2+y^2=16

Answer 2

R=4
r^2=4^2
r^2=16
r^2=x^2+y^2=16
x^2+y^2=16

Answer: Option (D) x^2+y^2=16