# Formula y=kx+n help

1. Homework Statement

Can somebody use the formula y=kx+n, to present me formula for the line which is parallel to the y axis and go among the point (-4,-5)?

2. Homework Equations

y=kx+n

3. The Attempt at a Solution

k=tg(alpha)

k=tg90

k=$$\frac{1}{0}$$

y=$$\frac{x}{0}$$

x=0

-4=0

Hm.....

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If the line is parallel to the Y AXIS then the slope has to be undefined, see why?

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rock.freak667
Homework Helper
1. Homework Statement

Can somebody use the formula y=kx+n, to present me formula for the line which is parallel to the y axis and go among the point (-4,-5)?

2. Homework Equations

y=kx+n

3. The Attempt at a Solution

k=tg(alpha)

k=tg90

k=$$\frac{1}{0}$$

y=$$\frac{x}{0}$$

x=0

-4=0

Hm.....
you can't multiply by zero like that.

If the line is parallel to the Y AXIS then the slope has to be 0, see why?
The y-axis is the vertical one,right?

wouldn't that be just x=-4?

rock.freak667
Homework Helper
That's what I believe it will be.

I know that it will be x=-4. But please prove it with y=kx+n
rock.freak667, y is the vertical one.

The problem is that the two assumptions

k, and n exist such that {(x,y): y=kx+n} is the set of points of the line

{(x,y): x = -4} is the set of points of the line

can not both be true.

what is k, what is n?

HallsofIvy
Homework Helper
I know that it will be x=-4. But please prove it with y=kx+n
rock.freak667, y is the vertical one.
You can't. A vertical line, parallel to the y-axis, cannot be written in that form.

You can't. A vertical line, parallel to the y-axis, cannot be written in that form.
Why?

HallsofIvy
Homework Helper
For exactly the reason everyone has been telling you! Writing "y= kx+ n" means that different values of x give different values of y. That is true for all lines except vertical lines. A line parallel to the y-axis has the same value of y for every x. When you learned "y= kx+n", the "slope-intercept" form, you should have learned that every non-vertical line can be written in that form but vertical lines cannot.

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Ahhh... I undertand now. Thank you very much.
btw- what is that same value for y?

HallsofIvy