Question

How do you use sum to product formulas to write the sum or difference `cos3theta+cos2theta` as a product?

Answer 1

`2cos ((5t)/2).cos (t/2)`

Explanation:

Use trig identity:
`cos a + cos b = 2cos ((a + b)/2)cos ((a - b)/2)`
In this case:
`cos ((a + b)/2) = cos ((5t)/2)`
`cos ((a - b)/2) = cos (t/2)`
There for:
`cos (3t) + cos (2t) = 2 cos ((5t)/2).cos (t/2)`