When two lines are perpendicular to one another, their slopes multiplied together is always going to be -1.
With this in mind, set up the following equation:
m₁ * m₂ = -1
[tex] \frac{5}{2} * m = -1\\
m=- \frac{2}{5} [/tex]
So [tex] - \frac{2}{5} [/tex] is your slope.
Since y = (-1)x + b, plug in y and x to solve for b, using the point (10, -8);
[tex] -8 = -1(10) +b\\
-10+b=-8\\
b=2 [/tex]
So your equation is y = -x + 2
