1. The problem is to draw a straight vertical line, which is a line at 90 degrees to the horizontal axis. 2. A vertical line has an equation of the form $x = a$, where $a$ is a constant number. 3. This means the $x$-coordinate is fixed and does not change, while the $y$-coordinate can be any value. 4. For example, the line $x = 5$ is vertical and passes through all points where $x$ is 5. 5. This line is not tilted; it is perfectly vertical, making a 90-degree angle with the $x$-axis. 6. To draw it, plot points like $(5, 0)$, $(5, 1)$, $(5, -2)$, etc., and connect them. 7. The key number that gives a vertical line is the constant $x$ value in the equation $x = a$. 8. Note that vertical lines cannot be expressed as $y = f(x)$ because they fail the vertical line test for functions.