Posted by Carmin on Wednesday, June 24, 2009 at 9:48am.
Which of the following is TRUE about the line through the points (–1, 4) and (–1, 2)?
Please EXPLAIN/SHOW WORK.
A. The slope is undefined
B. The slope is negative
C. The slope is 0
D. The slope is positive

Math  Carmin, Wednesday, June 24, 2009 at 9:49am
A. The slope is undefined.
B. The slope is negative.
C. The slope is 0.
D. The slope is positive.

Math  MathMate, Wednesday, June 24, 2009 at 10:35am
The slope m between two points P1(x1,y1) and P2(x2,y2) can be calculated using
m=(y2y1)/(x2x1) where x2≠x1
if x2=x1, and y2≠y1, it means that the line is vertical (slope is infinite or undefined)
if x2=x1 and y2=y1, the two points are coincident and the line is indefinite.
In all other cases, the slope m can be obtained by the formula above.
For the case in question,
P1(–1, 4) and P2(–1, 2)
so x2=x1=1, and y2≠y1
Therefore the line is vertical.
Post again if you need more explanations to choose the answer.

Math  Carmin, Wednesday, June 24, 2009 at 11:40am
If the line is vertical there is no slope making it undefined correct?

Math  MathMate, Wednesday, June 24, 2009 at 6:35pm
correct!

Math  MathMate, Wednesday, June 24, 2009 at 6:36pm
Sorry, it should read:
If the line is vertical the slope is infinite making it undefined.
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