Question

Find all solutions to 5cosθ = 3cosθ - 1.

Answer 1

hello : 
5cosθ = 3cosθ - 1.   
5cosθ - 3cosθ = 1.
2cosθ =1
cosθ =1/2
all solutions : 
 cosθ =cosπ/3
all solutions :
θ =π/3 +2kπ     or θ = - π/3 +2kπ ....k in Z