Question 49042
If you have two points, you can determine the equation of a line in the form of y=mx+b, where m is the slope.  The slope, m, is defined as {{{m=(y[2]-y[1])/(x[2]-x[1])}}}.  It doesn't matter which ordered pair is {{{x[1]}}},{{{y[1]}}} and {{{x[2]}}},{{{y[2]}}} because you'll get the same answer.  Using substitution we get {{{m=(5-3)/(7-8)}}} which reduces to m=-2.  So our formula so far is y=-2x+b.  To find out what b is, substitute one of your points (both x and y) into the equation; using the first ordered pair we get 5=-2*7+b, which simplifies to b=19.  So the equation is y=-2x+19.  Note that you'll get the exact same if you were to use the other ordered pair.<br><br>Because you need the equation with D and P instead of x and y, the formula becomes {{{P=-2D+19}}}.