Find the integrals of the functions.
∫1cos(x−a)cos(x−b)dx.
∫1cos(x−a)cos(x−b)dx=1sin(b−a)∫sin(x−a)−(x−b)cos(x−)cos(x−b)dx
Multiply by sin (b-a)in numerator and denominator both and sin (b-a)=sin [(x-a)-(x-b)].
=1sin(b−a)∫sin(x−a)cos(x−b)−cos(x−a)sin(x−b)cos(x−a)cos(x−b)dx[∴sin(C−D)=sinCcosD−cosCsinD]=1sin(b−a)∫[sin(x−a)cos(x−b)cos(x−a)cos(x−b)−cos(x−a)sin(x−b)cos(x−a)cos(x−b)]dx=1sin(b−a)∫(tan(x−a)−tan(x−b))dx=1sin(b−a).{−log|cos(x−a)|+log|cos(x−b)|}+C.|∴∫tanxdx=−log|cosx||=1sin(b−a)log∣∣cos(x−b)cos(x−a)∣∣+C