Honors Precalculus Notes--Chapter 5, Analytic Trigonometry

, 5. 2 Sum and Difference Formulas

The Cosine of the Difference of two Angles


T T
- -
-
-




Example
53
We know that cos 300=-2 .
Obtain this exact value
using cos 300 =
cos ( 900 600 )
-

and the difference formula for cosines .




Costa B )
cosdcosB-isindsin.BR
-
- -




B

900cos 600 900 sin 600
'


l
cos
-

+
sin l



E is
Ez )
'
(
-




)

3=0
=
(O .
z + 1. 3



I
+ 2


53
-

=
2 53
-


3
- E
3


I 1


r
Example us


Find the exact value of cos 700 cos 400-1 sin 705in 400



Costa B ) Costco SB + Sind sin .B
-
- -




cos (700-400) 1300 )
-




cos
-




is
= 2-




Sum and Difference Formulas for Cosine and sines