1.4
Evaluating Trig Functions:
Exact and Approximate Values
JMerrill, 2009
Exact

Recall: 30o-60o-90o Triangles

Example on Board
Trig Values – See page 39
Approximate Values

sin 75o ≈ 0.9659

tan 67o ≈ 2.3559

sec 52o ≈ 1.6247
Revolutions & Partial Degrees




A common unit for measuring very large angles is the
revolution, a complete circular motion (360o).
A common unit for measuring smaller angles is the
degree, of which there are 360 in one revolution. So, ¼
of a revolution is 90o.
Angles are more precisely measured by dividing 1
degree into 60 minutes and 1 minute into 60 seconds.
This gives us very precise locations in any space
(latitudes and longitudes).
Example: 25 degrees, 20 minutes, 6 seconds is written
25o20’6”
Degrees Con’t

To do by hand:


You try:


25o20’6” =
43o28’12”=
'
"
 20   6 
o
o
25  


25.335
 

60
3600

 

'
"
 28   12 
o
43o  
 
  43.47
 60   3600 
Now, let’s look at these same 2 problems and
do them on the calculator. You will use the
Angle menu (2nd apps).
Add/Subtract in DMS



35o21’42”
+ 7o 5’30”
42o26’72” which changes to 42o27’12”
Converting to DD

Convert 17o39’22” to decimal degrees.
Round to the nearest thousandth

17.656o
Evaluate

sin (18o10’)


≈ .3118
sec (20.524o)

≈1.149