1. 6.4 Product / Sum Identities

2. Product / Sum Identities
Product / Sum Identities have 2 forms! - They can be derived by adding or subtracting the sum or difference identities.
Product / Sum Identities

3. Alternate Form

4. Ex 1) Express the product as a sum or difference.

5. Ex 2) Express the sum as a product.
what happened to the (–) ?
cos is even
cos (–x) = cos (x)
and just in case …
sin is odd sin (–x) = – sin (x)

6. Try with a partner!!
Ex 3) Prove:

7. Homework
#603 Pg #1–17 odd, 21–23, 25–27, 38, 40, 44, 45
HW Hints & Even Answers:
21 & 22: eqtn you need is in paragraph above question – read!!
22: 15.9°
26 & 27: (proof  - start on RHS & use identities from section 6-1)
38:
40:
44 & 45: (proof  - start on LHS and use fact that you can divide both sides of identity by 2)
use the alternate form of product/sum identities