Question
Find general value of x, when cos x = cos y
Solution
We have cosx = cosy or cosx - cosy = 0
either 
or 
either 
or 
where 
either 
or 
where 
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or 
, where 
where 
Hence, the general solution is 
COROLLARY: If secx = secy 
cosx = cosy
So, when secx = secy, the general solution of 
where 
