To plot a straight line you need 2 points (x1,y1) and (x2,y2).
Assuming you want to show the the intersection of 2 lines, first calculate where they intersect. Let this be (Xi, Yi). To find the values, set the y's equal and solve for x. So, with a little algebra, you'll get
Xi=(b2-b1)/(m1-m2) and Yi=m1*(b2-b1)/(m1-m2)+b1...I think
Now, put 2 points for each line in the layout (*)
Code:
x11 y11 x21 y21
x12 y12 x22 y22
Select the data in the first 2 columns and cick the chart wizard. In step 1 create a XY Scatter chart (for the subtype select one with connecting lines). In step 2 make sure XL knows the data are in columns and that column 1 contains X values.
Once the chart is done, select and drag the second set on to the chart. In the dialog box that pops up make sure XL knows the data are in columns and the 1st column contains X values.
(*) As a refinement, you may want to include the intersection point. Suppose (Xi, Yi) is in the first quadrant (both x and y are positive). Then, you may want to plot
Code:
0 b1 0 b2
Xi Yi Xi Yi
2*Xi Y12 2*Xi Y22
Edit: As far as Q2 goes, there is no elegant solution. You have already been referred to both approaches that I know (the one documented by John Walkenbach and the other from Stephen Bullen).
Two part question and TIA
1) How can I graph 2 lines (both of the form y=mx+b, where I have both m's and both b's) on the SAME GRAPH?
and
2) How can I (or should I say can I) put this graph in a User Form?
Gene, "The Mortgage Man", Klein