If `x^2-2cosalphax+1=0` and `y^2-2cosalphay+1=0` then `2cos(alpha+beta)=`

If x^(2)-2cos alpha x+1=0 and y^(2)-2cos beta y+1=0 then 2cos(alpha+beta) is equal to (i)((x)/(y))+((y)/(x))(ii)(x+(1)/(y))(y+(1)/(x))(iii) (iv) none of these

If A=cos^(2)alpha+cos^(2)(alpha+beta)-2cos alpha cos beta cos(alpha+beta) then (i) A>1 (ii) 0<=A<=1 (iii) -1<=A<0 (iv) A<-1

If cos alpha =1/2(x+1/x),cos beta=1/2(y+1/y) then evaluate cos(alpha-beta)

If x cos alpha + y sin alpha = x cos beta + y sin beta "then" (2(1-cos (alpha - beta)))/(cos beta - cos alpha)^(2)=

Let x+1/x=2cos alpha, y+1/y=2cos beta z+1/z=2cosgamma."Show that"2 "cos"(alpha+beta+gamma)=xyz+1/(xyz)

If cos alpha+cos beta=0=sin alpha+sin beta. Prove that cos2 alpha+cos2 beta=-2cos(alpha+beta)

If cos alpha=(2cos beta-1)/(2-cos beta),0

If |{:(1,cos alpha, cos beta),(cos alpha, 1 , cos gamma ),(cos beta, cos gamma , 1):}|=|{:(0,cos alpha, cos beta),(cos alpha , 0 , cos gamma),(cos beta, cos gamma, 0):}| then the value of cos^2 alpha + cos^2 beta + cos^2 gamma is :

If alpha and beta are the roots of x^(2) - (a+1)x + 1/2 (a^(2) + a+1) = 0 then alpha^(2) + beta^(2) = "_____" .

If 2 cos alpha = x + (1)/(x) and 2 cos beta = y + (1)/(y) , show that (x)/(y) + (y)/(x) = 2 cos( alpha - beta)