Ok, so
We got the polar equation: r = 4
Remember that an equation in polar form, can be written in rectangular form using the following:
x = r cos Θ
y = r sin Θ.
And, x² + y² = r²
If we know that r=4, the answer is simple:
We know that x² + y² = r², so if we replace:
x² + y² = (4)²
And this is:
x² + y² = 16.
So, the answer is C.
