SOLUTION: Find cos (theta) and sin (theta) if the terminal side of (theta) lies along the line y = - 2 x in quadrant IV.

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Question 383273: Find cos (theta) and sin (theta) if the terminal side of (theta) lies along the line y = - 2 x in
quadrant IV.
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
If the terminal side of theta lies along the line y = - 2 x in
quadrant IV, then tan%28theta%29+=+y%2Fx+=+-2. From the identity 1%2B%28tan%28theta%29%29%5E2+=+%28sec%28theta%29%29%5E2, we get %28sec%28theta%29%29%5E2+=+5, or sec%28theta%29+=+sqrt%285%29, since secant is positive in the 4th quadrant. Then cos%28theta%29+=+1%2Fsqrt%285%29. From this we get sin%28theta%29+=+-2%2Fsqrt%285%29.