SOLUTION: prove that : 2 (cos^2)A+ cos A - 1 = 0

Algebra ->  Trigonometry-basics -> SOLUTION: prove that : 2 (cos^2)A+ cos A - 1 = 0      Log On


   

Question 921419: prove that :
2 (cos^2)A+ cos A - 1 = 0
Found 2 solutions by stanbon, Alan3354:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
2 cos^2(A)+ cos(A) - 1 = 0
-----
Factor:
(2cos(A)-1)(cos(A)+1) = 0
-----
cos(A) = 1/2 or cos(A) = -1
----
A = +/- 60 degrees OR A = 180 degrees
---------------
Cheers,
Stan H.

Answer by Alan3354(69443) About Me  (Show Source):