slope is calculate using the following equation:
slope = (y2-y1) / (x2-x1)
since the slope is undefined, therefore, the denominator is equal to zero, which means that x2 = x1.
Based on this, the only curves with undefined slopes are the curves with equation: x = constant
Therefore, equation of a line passing through a point (5,-3) with and undefined slope is x = 5
