I'm having trouble helping someone with there homework

queation: find the equation of the line that has no y intercept, has an x intercept of 4, and who's slope is undefined

y+mx+b
since b is y intercept and there is none that is 0 and disappears so next I used the points (4,0) to plug into formula

0=m4
0/4=m

that is not possible so what would be the equation of the line

:-)

You don't need that equation. It's a straight verticle line at x = 4.

Think about it. If it's a "line" (linear) and has no y intercept, it can't tilt either direction or it will eventually run across the y line. So it has to be verticle. And where? At x = 4.

Change in y over change in x: there's no change in x, putting a zero in the denominator. Undefined.

'vertical'.

Great answer. Checkout They have a detail explanation of slope

http://www.thexorb.com/Algebra/Slope/Slope-Calculation.aspx