## Sup_open~study 3 years ago Use the formula for slope to verify that a horizontal line has a slope of zero and that a vertical has an undefined slope. I have no idea what to do can some one help explain it to me thanks. :)

1. hartnn

The slope of the line through points (x1,y1) and (x2,y2) is given by : $$\huge m=\frac{y_1-y_2}{x_1-x_2}$$ now horizontal line has equation of the form y=c, here xterm has '0' co-efficient take any two points on this, say (x1,c),(x2,c) so put y1 = c and y2 = c in m and tell me what u get.

2. Sup_open~study

i'm sorry i don't get what the y = c part ??

3. hartnn

i'll draw a horizontal line|dw:1348817053391:dw| can u see that y-co ordinate of every point on that line is same??

4. Sup_open~study

yes

5. hartnn

that means for any value of x-coordinate , y co-ordinate will be some constant 'c' only.....so we can write its equation as y=c got this?

6. Sup_open~study

i think so the y will stay the same ( constant) meaning y = c ??

7. hartnn

yup. similarly for vertical line , the equation is x=c

8. Sup_open~study

i don't get the x=c part ??

9. hartnn

|dw:1348817443207:dw| can u see that x-co ordinate of every point on that vertical line is same

10. Sup_open~study

one is smaller than the other ??

11. Sup_open~study

so they are not really the same ??

12. hartnn

for a vertical line, x co-ordinate always remains constant. hence its equation can be written as x=c did u understand this?

13. Sup_open~study

yes i think i kind of get what what you are saying

14. hartnn

now reply to my first comment

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