Find the value of the following.

cos 40^o 20’

We write cos 40° 20’ = cos 40° 18’ + 2’.

The relevant part of the cosine table is given below.

From the table, we have

cos 40° 18’ = 0.7627

Mean difference for 2’ = 0.0004

We know that mean difference is to be subtracted in the case of cosine.

∴ cos 40° 20’ = 0.7627 - 0.0004 = 0.7623