Find the greatest possible value of

5cos(x)+6sin(x).

I know that it would be a good idea to look for identities that are in the form of acos(x)+bsin(x), but I can't seem to find any. Other than that I don't really know where to go with this problem. Any help would be much appreciated!

1 answer

Yes, there are lots of such formulas. One is at

http://www.uwfox.uwc.edu/users/tnyman/TRIGConcepts/Asinx+Bcosx.pdf

where you will see that the amplitude of your function is √(5^2+6^2) = √61