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CTK Exchange
Adrianne
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Jan-19-03, 09:13 PM (EST) |
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"equation for a vertical line"
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i need to find the equation for a vertical line... strictly going up and down, however i am having severe difficulties with it... please help |
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RicBrad
Member since Nov-16-01
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Jan-20-03, 09:12 AM (EST) |
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1. "RE: equation for a vertical line"
In response to message #0
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>i need to find the equation for a vertical line... strictly >going up and down, however i am having severe difficulties >with it... please help How about x = 3? I presume what you want is an equation of the form y = mx + c However this is not possible for a vertical line: just have a think about it - in the above example, what value does y take at x = 3? It takes many values, but a function can only give a single value for a single input, so y cannot be given as a function of x. You could also define the line parametrically: for any s, (s), y(s)) = (3, s) Hope this helps, Rich |
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bluediamond
Member since Apr-9-02
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Jan-20-03, 09:12 AM (EST) |
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2. "RE: equation for a vertical line"
In response to message #0
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Assuming that you are talking about the Cartesian plane, then an equation describing a vertical line isn't too difficult; it's simply x = c, where c is some constant. For example, x = 2 would describe a line passing through (2,0). However, there is no _function_ for a vertical line because functions must map a point in the domain to only one point in the range. In this case, x represents values in the domain, and y represents values in the range. A vertical line, such as x = 2, would map the value 2 in the domain to more than one point in the range; in fact, it maps 2 to every single value in the range, thus contradicting the definition of a function. Hope this helps, Dave |
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MrU
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Jan-20-03, 07:00 PM (EST) |
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4. "RE: equation for a vertical line"
In response to message #0
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If you follow many common steps for writing the equation of a line, you would start with the formula for slope. Since any vertical line has all points with the same "x" value, your slope slope has a denominator of zero. The slope, therefore, does not exist. As a teacher, my advice to all students learning to write the equations of vertical and horizontal lines is to accept them as they are: special cases that deserve special attention (like learning idioms in a foreign language). |
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alexb
Charter Member
911 posts |
Jan-20-03, 07:10 PM (EST) |
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5. "RE: equation for a vertical line"
In response to message #4
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>If you follow many common steps for writing the equation of >a line, you would start with the formula for slope. Not necessarily. Why not start with a more general equation (*) ax + by + c = 0 >Since >any vertical line has all points with the same "x" value, >your slope slope has a denominator of zero. There's no need to say that. If one can't divide by 0, how is it possible for a denominator to be 0? Say, find the equation of the line with points (2,1) and (2,3) lie on on it. 2a + b + c = 0 2a + 3b + c = 0 Therefore b = 0, while a could be taken to be 1 and c -2. The equation becomes x - 2 = 0 No reason to mention the slope at all. >The slope, >therefore, does not exist. Right. >As a teacher, my advice to all students learning to write >the equations of vertical and horizontal lines is to accept >them as they are: special cases that deserve special >attention (like learning idioms in a foreign language). It could be useful to mention that "being vertical" is nothing but "being parallel to the y-axis" and similarly for "being horizontal". The moment the plane is rotated even a little bit, the vertical lines cease to be exceptions. Exceptions arise not because lines are vertical or not, by because the coordinate system is usually so chosen as to be formed by a vertical and a horizontal line.
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