- #1
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Homework Statement
Find the exact value, without using a calculator.
[tex] \ cos(\frac{\pi}{15}) \ cos(\frac{\pi}{45})[/tex]
The Attempt at a Solution
I started off using a product to sum formula-
[tex]\frac{1}{2}[cos(\frac{4\pi}{45})+ \ cos(\frac{2\pi}{45})][/tex]
Now I don't know where to go. I'm trying to use a sum/difference formula, but I can't find two values from the unit circle that will add or subtract to the arguments of the cosines, so I'm thinking that's not the best way to go. I tried using a sum to product formula within the product to sum formula, but then I realized that it was just going to get me back to the original expression pretty quickly. I tried the half angle formulas, but those still don't get me to a value that's on the unit circle.
Any suggestions?