SOLUTION: 9 cos^2 theta + 3 cos theta =0, where 90 degrees < theta < 180 degrees, what is the value of theta, correct to the nearest tenth? This is what I did but my answer is wrong cause it

Algebra ->  Trigonometry-basics -> SOLUTION: 9 cos^2 theta + 3 cos theta =0, where 90 degrees < theta < 180 degrees, what is the value of theta, correct to the nearest tenth? This is what I did but my answer is wrong cause it      Log On


   

Question 279481: 9 cos^2 theta + 3 cos theta =0, where 90 degrees < theta < 180 degrees, what is the value of theta, correct to the nearest tenth? This is what I did but my answer is wrong cause it's suppose to be in degrees.9 cos^2 theta + 3 cos theta =0 Then I subtracted 3 cos theta from both sides so 9 cos^2 theta= -3 cos theta Then I divided both sides by cos 3 theta so cos theta = -1/3. I don't think I understand how to do the question since it's not in degrees. Any ideas?? Thanks
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
theta is in the 2nd quadrant

what angle in the second quadrant has a cosine of -1/3?

your calculator must have an inverse cosine function ___ cos^-1

theta = 109.5º