SOLUTION: Rewrite as a single expression. cos(9theta)cos(6theta)-sin(9theta)sin(6theta) Select one: a. cos(15theta) b. sin(14theta) c. sin(6theta) d. cos(14theta)

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Question 1087889: Rewrite as a single expression. cos(9theta)cos(6theta)-sin(9theta)sin(6theta)
Select one:
a. cos(15theta)
b. sin(14theta)
c. sin(6theta)
d. cos(14theta)
Found 2 solutions by Alan3354, ikleyn:
Answer by Alan3354(69443)   (Show Source): You can put this solution on YOUR website!
Check "Half angle formulas" on Wikipedia.
Answer by ikleyn(52812)   (Show Source): You can put this solution on YOUR website!
.
Rewrite as a single expression. cos(9theta)cos(6theta)-sin(9theta)sin(6theta)
Select one: 

a. cos(15theta)    <<<---=== This and only this (9 + 6 = 15).

b. sin(14theta)

c. sin(6theta)

d. cos(14theta)


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