Question

find the general solution of cos(x+π/10)=0

Answer 1

Cos A  = 0  the general solution is
    A =  n π + π/2  or   n π - π/2        where n is an integer

Cos (x + π/10) = 0
  =>  x + π/10 = n π + π/2    or  n π - π/2
  =>  x =  n π + 2 π/5      or    n π - 3 π/5
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Or,
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Cos A = 0  has a general solution of 
    A = (2 n + 1) π/2      where n an integer (+ve or negative)

hence,  Cos (x + π/10) = 0 has the solution of
   x + π/10 =  (2 n + 1) π/2
   x = n π + 2π/5        where n is an integer.