Find all solutions in the interval [0,2pi):
cos2x + 5cosx = 2
We have the equation cos2x + 5cosx = 2
We use the identity cos2x=2(cosx)^2-1 here.
Then the equation becomes
2(cosx)^2-1+ 5cosx = 2==>2(cosx)^2+5cosx-3=0.
Observe that 2 x (-3)=-6. Write -6 as product of two ...
Solving Trigonometric Identities on an Interval is investigated.