Actually 20/60 x .00020 = .0000666.

But rounding off .0000666 to five

places is .00007.

Therefore, cos 43,, 20' 20" = .72737 - .00007 = .72730.

b.

In the next example, the process varies slightly. It is necessary to

subtract the difference from the value of the smaller angle. This is true

in the case of all cofunctions because their values decrease as the angle

increases.

The process varies slightly when an angle is desired from a

given function.

EXAMPLE

Find the angle whose sine is .68420.

SOLUTION

sin 43,, 11' = .68434

sin x

= .68420 (unknown angle)

sin 43,, 10' = .68412

Difference between sin 43,, 10' and sin 43,, 11' = .00022.

Difference between sin 43,, 10' and sin x (unknown angle) = .00008.

From this the desired angle is

of the way

from 43,, 10' to 43,, 11';

Therefore, the desired angle is 43,, 10' 22".

c.

To get the value of the sine, cosine, tangent, or cotangent of an

angle between 45,, and 90,,, use the degrees at the bottom, as explained

below.

(1) Find the number of degrees at the bottom of the trigonometric tables

(see Tables 6 and 7, on pages 59 and 60).