Linear Equations with Only X or Y instead of BothDate: 04/09/2008 at 18:12:26 From: Jenny Subject: Linear Equations Without and X value or Y value Dr. Math, My math teacher didn't explain what to do if the linear equation only has one variable (X or Y) instead of both. We're supposed to find X in terms of Y. Ex: y + 2 = 0 Ex: 2x - 1 = 0 What are you supposed to do if you only have a X, or just a Y? How do you know if a linear equation is zero slope or unidentified? How are you supposed to graph a line that's zero or unidentified? Also, I have no idea of how to graph the line with only one point. Do you just create a straight line? Thanks! Jenny Date: 04/10/2008 at 09:06:38 From: Doctor Ian Subject: Re: Linear Equations Without and X value or Y value Hi Jenny, You can always use a coefficient of 0 for the "missing" variable. So y + 2 = 0 becomes 1y + 0x + 2 = 0 What does this tell us? It means that the value of y doesn't depend on the value of x. That's sort of the description of a horizontal line, isn't it? And in fact, if we try to solve for y, we get y = -0x - 2 which means the slope is zero... which is also one way to define a horizontal line. With the other example, 2x - 1 = 0 we can use the same idea to get 0y + 2x - 1 = 0 Looking at this, we see that the value of x doesn't depend on the value of y. That's the description of a vertical line, isn't it? And if we try to get the slope-intercept form, we get y = (-2/0)x + 1/0 and the slope is undefined. Which is another way to define a vertical line. Does that make sense? You wrote: >Also, I have no idea of how to graph the line with only one point. Do >you just create a straight line? You can use those equations to get more than one point. For example, 0y + 2x - 1 = 0 is true when x is 1/2 and y is 0, right? So (1/2,0) is one point on the line. It's also true when x is 1/2 and y is 1. So (1/2,1) is another point. In fact, if you just solve it for x, you get x = 1/2 which tells you that (1/2,anything at all) is a point on the line. So pick two of them, and fill in the graph as usual. Does this help? - Doctor Ian, The Math Forum http://mathforum.org/dr.math/ Date: 04/10/2008 at 18:11:55 From: Jenny Subject: Thank you (Linear Equations Without and X value or Y value) THANKS!!!!!!!!=) |
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