`cos x+cos y = 4/5, cosx - cos y = 2 /7 => 14 tan( (x - y )/ 2) + co t ((x + y) / 2)=`

cos x + cos y = (4) / (5), cos x-cos y = (2) / (7) rArr14tan ((xy) / (2)) + 5cot ((x + y) / (2)) =

Prove that cos ^ (- 1) ((cos x + cos y) / (1 + cos x cos y)) = 2tan ^ (- 1) (tan ((x) / (2)) tan ((y) / (2)))

prove that tan ((pi) / (4) + (1) / (2) cos ^ (- 1) ((a) / (b))) + tan ((pi) / (4) - (1) / (2) cos ^ (- 1) ((a) / (b))) = (b) / (a) cos ^ (- 1) ((cos x + cos y) / (1 + cos x cos y) ) = 2tan ^ (- 1) ((tan x) / (2) (tan y) / (2))

If sin x + sin y = 1/2 and cos x + cos y = 1 then tan (x + y)

If cos x+ cosy =(4)/(5) and cos x- cos y =(2)/(7) , then the value of 14 tan ((x-y)/(2)) +5 cot ((x+y) /2)

(cos x + cos y ) ^(2) + (sin x - sin y ) ^(2) = 4 cos ^(2) ""(x + y )/( 2)

(cos x + cos y ) ^(2) + (sin x - sin y ) ^(2) = 4 cos ^(2) ""(x + y )/( 2)

(cos x + cos y ) ^(2) + (sin x - sin y ) ^(2) = 4 cos ^(2) ""(x + y )/( 2)

(cos x + cos y ) ^(2) + (sin x - sin y ) ^(2) = 4 cos ^(2) ""(x + y )/( 2)

(cos x + cos y ) ^(2) + (sin x - sin y ) ^(2) = 4 cos ^(2) ""(x + y )/( 2)