[" 10.If "cos alpha+cos beta=cos(3 pi)/(7)" and "sin alpha+sin beta=sin(3r)/(7),b],[cos^(2)(a-beta)/(2)]

(cos alpha + cos beta) ^ (2) + (sin alpha + sin beta) ^ (2) =

If cos alpha + cos beta =cos ""(3pi)/(7)and sin alpha + sin beta = sin ""(3pi)/(7), then the value of cos ^(2)""(alpha-beta)/(2) is-

(cos alpha + cos beta) ^ (2) + (sin alpha-sin beta) ^ (2) = 4 (cos ^ (2) (alpha + beta)) / (2)

For alpha , beta in R , prove that (cos alpha + cos beta )^(2)+ (sin alpha + sin beta )^(2)=4cos^(2). ((alpha-beta))/(2)

If cos alpha+cos beta=0=sin alpha+sin beta then cos2 alpha+cos2 beta=

sin alpha+sin beta=(1)/(4) and cos alpha+cos beta=(1)/(3) The value of cos(alpha+beta) is

sin alpha+sin beta=(1)/(4) and cos alpha+cos beta=(1)/(3) The value of cos(alpha+beta) is