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=(y2-y1)/(x2-x1) 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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