Final answer:
A line perpendicular to the y-axis, containing the point (-5, 6), has the equation x = -5 and an undefined slope.
Step-by-step explanation:
A line perpendicular to the y-axis is a vertical line. Since this line contains the point (-5, 6), its equation will be x = -5. The slope of a vertical line is undefined because it does not change along the y-axis.