posted by ashely .
find the exact value of cos 3.14/8
Since 3.14 is an approximation to π,
I suppose you mean finding the exact value of cos(π/8).
Use the half angle formulae:
The second formula is not required for this problem, but I suggest you memorize both of them, because they will be very useful in your academic life.
Start from known values,
Apply the formula one more time to get cos(π/8):
Okay, I understand how to get pi/8 but how do you figure pi/7 and how do you figure cos(10degrees) when you can use the sum and difference method of angles? Please help it is driving me crazy, and I have finals coming up. Need to get this down. Can I do the method about using pi/3 and pi/4 in the half angle formulas to find exact value of cos and sin of (pi/7)? I am so confused.