First you draw a picture of angle s in quadrant III, and draw a perpendicular
from the end of the terminal side up to the x-axis.



You are given cos(s) = -1/6. You know that cosine = adjacent/hypotenuse,
which is x/r, so we label the x value as the numerator of -1/6, which
is -1, and we label the hypotenuse (the terminal side) as the denominator
of -1/6, which is 6. (The hypotenuse or terminal side is always taken
positive.



We use the Pythagorean theorem to find the value of y:







Since y goes down from the x-axis we give it a negative sign.
We label the opposite side, which is y, as -√35



We will need the sine and cosine of s,

 which is given, and





The same way, draw the angle t, and get this graph:



We will need the sine and cosine of t,

 which is given, and


Now we use the formula for 









Edwin