sec^2 a = tan^2 a + 1
sec a = 1 / cos a
Go from there.
Draw a triangle with y = -3a and x = 2a, and then calculate the value for r (the hypotenuse) by using the Pythagorean Theorem: . Since all basic trig functions are functions of some combination of x, y, and r, you should be able to calculate all of them once you know r.