Equation of a Line Parallel to an AxisDate: 06/19/2003 at 05:45:39 From: Barb Subject: Slope intercept How can I get the equation of a line if the line passes through a point and is parallel to the x- or y-axis? Ex: "if the line passes through (-3,-4) and is parallel to the y-axis" Date: 06/19/2003 at 09:50:11 From: Doctor Ian Subject: Re: Slope intercept Hi Barb, A horizontal line always has an equation that looks like y = [some constant] and a vertical line always has an equation that looks like x = [some constant] If I know that a horizontal line passes through the point (5,6), then I know that the value of y is the constant I want, so the equation must be y = 6 If I know that a vertical line passes through the point, then I need the value of x instead: x = 5 So in fact, we can be a little more precise, and say that a horizontal line has the equation y = [the y-value of any point on the line] while a vertical line has the equation x = [the x-value of any point on the line] What if you forget these equations? The quickest way to figure them out again is to draw a horizontal or vertical line, and start identifying points on it: x=4 | . | . | (4,12) | . | . | (4,9) | . | . | . .......(1,3).......(5,3)...........(11,3)..... y=3 | . ----+----------.------------------------------- | . | (4,-3) | . | . Does this make sense? - Doctor Ian, The Math Forum http://mathforum.org/dr.math/ Date: 06/21/2003 at 04:09:56 From: Barb Subject: Thank you (Slope intercept) Dr. Ian, Thank you for your help. I really appreciate this. I now understand how to get the line equation. Thanks again! |
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