Answer: Choice D)
No slope, the term x2-x1 is zero and we cannot have zero in the denominator.
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Step-by-step explanation:
The two points both have x coordinates x = 7. Since both x coordinates are the same, they subtract to 0. Recall that something like 1/0 is undefined, so we cannot have 0 in the denominator.
The line through (7,10) and (7,20) is a vertical line. All vertical lines have undefined slopes.