Question 21959: My line is (-7, 2) ; (-7, -2). Obviously this is a horizontal line. Also, this does not have a y-intercept. How would I find the equation of this line? In the formula y = mx+b, would "b" represent the x-intercept in this case? Thank you in advance!
Found 2 solutions by anjikumar, Earlsdon:
Answer by anjikumar(3)   (Show Source):
You can put this solution on YOUR website! You are right that the line (-7,2) ; (-7,-2) is a horizontal line which can be stated as (y=x).
Using the formula y=mx+b, the slope "m" is 0, since it is a horizontal line and "b" is where it intersects the y-axis, in this case, at -7.
Therefore, the equation of a horizontal line at -7, is y=x-7.
All horizontal lines will be written this way, for example, y=x+5, if it is at +5. y=x is basically the x-axis at y=0, so you can go up or down on the y-axis by adding or subtracting to that basic equation.
Answer by Earlsdon(6294) (Show Source):
You can put this solution on YOUR website! If your line is (-7, 2) ; (-7, -2) then the line is a vertical line (straight up-and-down) rather than a horizontal line (flat, side-to-side).
The equation of this line would be: x = -7 and, you are right, there is no y-intercept, only an x-intercept (x = -7), so the slope-intercept form has no meaning for such a line. Since the y-coordinate of this line can take on any value you please, the coordinate of any point on this line can be written: (-7, a), where a is any real number.
A vertical line has an undefined slope (m) and no y-intercept (b) so it cannot be represented by the slope-intercept form of the equation.
Also, the equation: y = x represents a line that is at 45 degrees to the axes and passes through the origin.
Here's the graph of y=x:
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