The other tutor gave you a correct answer, but he gave it as a sine
function of the complement of the reference angle, instead of
a cosine function of the reference angle. I think you should
express it as a cosine function of the reference angle, since
you were given a cosine function, not change to different trig
function.
Rules for finding the reference angle:
If an angle is between 0° and 90° (Quadrant I), the reference angle
is the same as the angle.
If an angle is between 90° and 180° (Quadrant II), to find the reference
angle, subtract it from 180°.
If an angle is between 180° and 270° (Quadrant III), to find the reference
angle, subtract 180° from it.
If an angle is between 270° and 360° (Quadrant IV), to find the reference
angle, subtract it from 360°.
So the reference angle for 136° (Quadrant II), is 180°-136° = 44°
Since the cosine is negative in Quadrant II, the answer is
-cos(44°)
That is what I believe your teacher wants, not a sine function of
the complement of the reference angle.
Edwin
