## Calculus: Early Transcendentals 8th Edition

The equation $x=5$ represents a vertical plane parallel to the yz-axis that is shifted 5 units in the positive x direction.
The equation sets a value for x that is independent of y or z. If $f(y,z)=x$, then $f(y,z)$ will equal 5 at every point on the yz-plane.