Question

If cos (A - B) =3/5
and tan A tan B = 2, then prove that :
cos A cos B=1/5​

Answer 1

Step-by-step explanation:

cos (A-B) =3/5

5cosAcosB+5sinAsinB=3

but from 2nd relation

sinASinB=2cosacosb

(5+10)cosAcosB=3

cozAcosB=1/5