Plotting Straight Lines

When you have the equation of a straight line, you can plot it by finding any two points on the line then connecting them.

But if you don't have the line equation, but do have enough information about a line, you can find the equation and therefore the line plot as well.

If you give two points or give one point and the slope, you can get the equation of the line and its plot.

1. Given any two points (X1, Y1) and (X2, Y2) to get a straight line:

   	X	Y
   point one:
   point two:

   What if someone tries to trick the plotting by giving it two points that are the same? Try that and see what happens.

2. Give a point and a slope to get a straight line:

   	X	Y
   point:
   slope:

3. Challenge: Given the equation of a line and a point (a, b), how do you determine if the point is on the line or not?

4. Can you find lines that can not be entered in the slope-point form? If indeed there are such lines, how can they be plotted then?