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Question 91415: What is the slope and the y-intercept of x= -9?
Answer by bucky(2189)   (Show Source):
You can put this solution on YOUR website! The graph of this equation [ x = -9] is a vertical line through -9 on the x-axis.
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[Think of it this way ... x is always -9 no matter what y is. Therefore, (-9,-10), (-9, 0),
(-9, 26) are all points on the graph. They all have x = -9 and therefore they all satisfy
the given equation x = -9.]
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Because the graph of this equation is a vertical line, it is parallel to the y-axis.
Therefore, there is no y-intercept. Do not say that the y intercept is zero. That is incorrect
because it does not mean the same as there IS NO y-intercept.
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The slope of this vertical line graph is undefined. Why is that? Slope is defined as:
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But the Run (the horizontal change) is zero. Therefore the Slope equation becomes:
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But division by zero is not allowed in algebra. Therefore, the slope is undefined.
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Also note that an undefined slope is NOT the same as a slope equal to zero. A line that
has a zero slope is a horizontal line, not a vertical line.
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Hope this helps you to understand the problem a little better.
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