It doesn't matter which way we choose *a* and *b*, so we'll do it both ways. First, take *a* to be the smaller of the two *x* values. Here *f* is the equation of the line. We don't know the equation of *f*, but we know both points are on *f,* which means *f*(3) = 15 and *f*(5) = 30. We have Then Second, flip *a* and *b*. Then so We find the same value for slope either way. |