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

If cos(x-y), cosx and cos(x+y) are in H.P., then |cos x sec (y)/(2)| equals

If cos(x-y),cosx and "cos"(x+y) are in H.P., then cosxsec(y/2) is

If cos (x-y),, cosx and cos(x+y) are in H.P., are in H.P., then cosx*sec(y/2) =

If 2(cos(x-y)+cos(y-z)+cos(z-x))=-3 , then :

lf cos x + cosy-cos z = 0 = sin x + sin y + sin z then cos((x-y)/2)=

If cos x+cos y-cos(x+y)=(3)/(2) , then

If cos ^(-1)\ (x)/(a) + cos^(-1)\ (y)/(b) = theta , then (x^(2))/(a^(2)) +(y^(2))/(b^(2))=?

If y= sin x+cos x then (d^(2)y)/(dx^(2)) is :-

If cosx + cosy + cosz = 0 and sinx + siny + sinz =0 , then show that cos (x-y) + cos(y - z) + cos(z - x) = - 3/2.

If cos(y-z)+cos(z-x)+cos(x-y)=-3/2, prove that cos x + cos y + cos z = 0 = sin x + siny + sinz.