How can we write an equation for a line that does not go pass the y-axis ? What would the "b" in the equation be ?

The slope intercept form of a line is given as :

y = mx + b

where, m is the slope of the line and b is the y-intercept (value of y when x = 0, or when line crosses the y-axis). 

If a line does not intersect y-axis, then it is parallel to y-axis or perpendicular to the x-axis. In this case, at every point of the line, the y-coordinate will be equal to...

The slope intercept form of a line is given as :

y = mx + b

where, m is the slope of the line and b is the y-intercept (value of y when x = 0, or when line crosses the y-axis). 

If a line does not intersect y-axis, then it is parallel to y-axis or perpendicular to the x-axis. In this case, at every point of the line, the y-coordinate will be equal to 0. 

Hence, for a line that does not intersect the y-axis, the value of y-intercept (b) would always be 0. 

Similarly, the slope of the line will be undefined, since the slope is given as (y2-y1)/(x2-x1) or, (y2-y1)/0.

In fact, the slope-intercept form of the line equation does not work for this particular case: case of a vertical line.

Hope this helps.