Let us start subtracting 3 cos theta both sides so that we may get all theta terms on left side only
It is now : 4 cos theta - 3 cos theta = - (sqrt3)/ 2
1 cos theta = -( sqrt 3 ) /2
we know cos (pi-x)= - cos x And cos (pi+ x)= - cos (x)
********* let us first use :
- Cos ( pi - theta) = - ( sqrt 3 )/2
this implies cos (pi- theta )= (sqrt 3) /2
cos ( pi - theta )= cos (pi /6)
pi- theta = pi/6
pi- pi/6 = theta
5 pi/6 = theta
one of teh answer is 5 pi/6 . another value of theta would be :
(2pi - 5pi/6)= 7pi/6
Answer: 5 pi/6 and 7 pi/6
