Question

cos α =3/5

cos β = 4/5

find value of cos( α - β)/2


assuming α and β to be acute angles

Answer 1

as we know

if cos alpha = 3/5

then alpha = 53

and cos beta = 4/5

that means beta = 37


So cos ( alpha -beta)/2 = cos( 53-37)/2 = cos 16/2 = cos 8 =0.99