SOLUTION: If cos A= -4/5 for angle A in Quadrant II, find tan A/2 I'm doing this on A+LS it's giving me a lot of trouble the answer, how to do it, plus alternate forms would really be apprec

Algebra ->  Trigonometry-basics -> SOLUTION: If cos A= -4/5 for angle A in Quadrant II, find tan A/2 I'm doing this on A+LS it's giving me a lot of trouble the answer, how to do it, plus alternate forms would really be apprec      Log On


   

Question 1099978: If cos A= -4/5 for angle A in Quadrant II, find tan A/2 I'm doing this on A+LS it's giving me a lot of trouble the answer, how to do it, plus alternate forms would really be appreciated even when I have the right answer sometimes it registers as wrong.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+cos%28+A+%29+=+-4%2F5+
The angle is in the 2nd quadrant
cos is negative
sin is positive
tan is negative
+tan%28+A%2F2+%29+=+%28+1-cos%28A%29+%29+%2F+sin%28+A+%29+
+tan%28+A%2F2+%29+=+%28+1+-%28-4%2F5%29+%29+%2F+%28+3%2F5+%29+
+tan%28+A%2F2+%29+=+%28+5%2F5+%2B+4%2F5+%29+%2F+%283%2F5%29+
+tan%28+A%2F2+%29+=+%28+5+%2B+4+%29%2F3+
+tan%28+A%2F2+%29+=+3+
( note that +A%2F2+ is in the 1st quadrant )