If `cos(x-y)=1` then `cos x + cos y=`

If cos x+cos y=1 and cos x cos y=(1)/(4) then the G.S are

If cos (x-y) , cos x , cos (x+y) are three distinct numbers which are in harmonic progression and cos x ne cos y , " then " 1+ cos y =

If cos(x -y) , cos x and cos(x + y) are in HP then cos x* sec (y/2) = ________.

If cos(x - y)= -1 , show that cos x + cos y = 0 and sin x + sin y = 0 .

If cos x.cos y + sin x.sin y = -1 then cos x + cos y is यदि cos x.cos y + sin x.sin y = -1 हो, तो cos x + cos y का मान क्या होगा?

If (sin x) (sin y) = 1, then (cos x) (cos y) =?

If cos (x-y) =-1, then the values of (cos x+ cos y) and (sin x + sin y) are respectively-