Answer:
x = 4
Explanation:
You want the equation of a line that goes through point (4, 0) and has an undefined slope.
Undefined slope
The slope of a line is the ratio of "rise" to "run." When the "run" is zero, the ratio involves division by zero, which results in the value "undefined." That is, a line with undefined slope has a "run" of zero, meaning it is a vertical line.
The equation for a vertical line is ...
x = c . . . . . where c is some constant
We want the line to go through a point that has x-coordinate = 4, so that constant must be 4.
The equation is x = 4.