



 
Hi Ellen. You're right: b is 1. You get this by noting that the first line must pass through (4, 6) so substitute 4 and 6 in for x and y in the first equation to solve for b:
Two lines on a graph that meet at right angles are perpendicular to each other, so their slopes are the negative reciprocal of one another. For example, if the slope of one line is m, then the slope of the other is 1/m. Let's rewrite the lines in y=mx+b form to reveal the slopes:
So if these slopes are the negative reciprocal of one another,
Now you can solve for a. And with the values for a, x, and y, you can easily find the remaining unknown c by substituting these values into the equation for the second line. Hope this helps,  


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. 