You can put this solution on YOUR website! Express the value as a trigonometric function of an angle in quadrant 1.
cos1290
-----
I'm going to assume that is 1290 degrees.
-----
1290/360 = 3.5833 = 3*360 + 0.5833*360
Note: We can drop the 3*360 ; that leaves us with 0.5833*360
---
0.5833*360 = 210 degrees
------
The reference angle for 210 degrees is 210-180 = 30 degrees
----
Note: 210 is in QIII where cos is negative.
---
Ans: cos(1290) = cos(210) = -cos(30)
------------------
Cheers,
Stan H.
---------------
(