1. SUM & DIFFERENCE FORMULAS

2. SUM & DIFFERENCE FORMULAS cont’d.

3. Ex. Use the sum & difference identities to find the EXACT value
of each function…this means answers will be fractions perhaps
with Radicals…NOT decimals!
1. cos 75˚

4. Ex. Use the sum & difference identities to find the EXACT value
of each function…this means answers will be fractions perhaps
with Radicals…NOT decimals!
1. cos 160˚cos40˚+sin160˚sin40˚
A 120˚ is a 60˚ in the 2nd quadrant.

5. Ex. If A & B are the measures of two first quadrant angles,
find the exact value of each function.
1. If sinA=12/13 and cosB=3/5 , find cos (A-B). 13 12 5 4 A B 5 3
Recall: cos (A-B)=cosAcosB+sinAsinB
So, we need:
CosA & sinB
which means we use pythag. Thm.
122+b2=132
results in b=5
So, cosA=
5/13
a2+32=52
results in a=4
So, sinB=
4/5
cos (A-B)=(5/13)(3/5)+(12/13)(4/5)
cos (A-B)=63/65

6. Ex. Use the sum & difference identities to find the EXACT value
of each function…this means answers will be fractions perhaps
with Radicals…NOT decimals!
2. tan 345˚

8. DOUBLE- & HALF-ANGLE FORMULAS.
Double Angle or

9. DOUBLE- & HALF ANGLE FORMULAS cont’d