Question 928623
2 (sin x)^2-5 cos x - 4 = 0.
 ------
2(1-cos^2)-5cos - 4 = 0
-------
2 - 2cos^2 - 5cos - 4 = 0
-----
2cos^2 + 5cos +2 = 0
----
Factor::
(2cos+1)(cos+2) = 0
---
cos(x) = -1/2 or cos(x) = -2
-------
cos(x) = -2 implies x = (2/3)pi or (4/3)pi
----
cos(x) = -2 is extraneous
==============================
Cheers,
Stan H.
-------------------