The equation \( r = 5 \) represents a circle in polar coordinates, where \( r \) is the radius. To convert this to rectangular form, we can use the relationship \( r^2 = x^2 + y^2 \).
So we have:
\[ r^2 = 5^2 \]
This simplifies to:
\[ x^2 + y^2 = 25 \]
Thus, the correct rectangular form is:
x squared plus y squared equals 25.