A line that includes the points (d,4) and ( – 4, – 5) has an undefined slope. What is the value of d?

Answer 1

A vertical line has an undefined slope.

The equation of a vertical line is in the form x = h

Since the line passes through (-4, 5) d = -4

Answer 2

Slope = (-5-4) / (-4-d) = -9 / (-4-d)

Slope is undefined if the denominator = 0

So, undefined slope when d = -4 (that is, the 2 points lie on a vertical line)