If sin α – sin β = a and cos α + cos β = b, then write the value of cos (α + β).
sin α – sin β = a
cos α + cos β = b
(sin α – sin β )2= a2 …..1
(cos α + cos β)2= b2 …….2
add both equations
value of 
1
If sin α – sin β = a and cos α + cos β = b, then write the value of cos (α + β).
sin α – sin β = a
cos α + cos β = b
(sin α – sin β )2= a2 …..1
(cos α + cos β)2= b2 …….2
add both equations
value of