1) First we need to find the slope of l1 . Let's get its equation into slope-intercept form.
5x + 8y = -9 Subtract 5x from both sides of the equation.
8y = -5x - 9 Divide through by 8 .
y = -\(\frac58\)x - \(\frac98\)
Now we can see that the slope of l1 = -\(\frac58\) .
Line l2 is perpendicular to l1 , so the slope of l2 = +\(\frac85\) .
Line l2 has a slope of \(\frac85\) and passes through the point (10, 10) .
So.... in point - slope form, the equation of l2 is
y - 10 = \(\frac85\)(x - 10) We want this in the form y = mx + b . Distribute the \(\frac85\) .
y - 10 = \(\frac85\)x - \(\frac85\)(10)
y - 10 = \(\frac85\)x - 16 Add 10 to both sides.
y = \(\frac85\)x - 6
Now the equation for l2 is in the form y = mx + b , where m = \(\frac85\) and b = -6 .
We can look at a graph to verify that l1 and l2 are perpendicular, and l2 passes through (10, 10) .
m + b = \(\frac85\) + -6 = -4.4