Do you know either the "double angle formulas" or the "half angle formulas"?
If cos2x=12/13 and 2x is in the first quadrant, evaluate the six trigonometric functions for x, without your calculator. The answer is:
cos x= 5/√26; sec x=√26/5
sinx=1/√26; csc x=√26
tanx=1/5; cot x=5
How do I get these answers? Any help would be greatly appreciated.