Hi,

First of all thanks for your reply. Here is another question about trigonometric equation.

Solved Example:

cos^(x) + cos (x)= sin^x on 0 degree < x< 360

cos^(x) + cos (x)= 1-cos^(x)

2cos ^(x) + cos (x)-1= 0

(2cos(x) -1)(cos(x) + 1= 0

cos(x)=1/2 , cos x = -1

so complete solution is

60 degree,180 degree, 300 degree.

AS from reference angle , I know that cos 1/2 = 60 degree .But how did the book get the complete solution like 180 and 300 degree .(from where came the 180 and 300 degree)