Every point on the line has x coordinate 15 that is why its equation is x 15. And where does it cross the Y-Axis. An undefined slope indicates that we have a vertical line parallel to the y-axis and passing through all points in the plane with an x-coordinate constant c The equation is written in the form x c.
In fact this is a special case and we use a different equation like this.
An undefined slope or an infinitely large slope is the slope of a vertical line. Undefined slope if a line y mx b y m x b is vertical. These lines are always of the form x c where c is some number. This is often stated as The slope of the line is undefined or as The line has no slope.