Thread: Trigonometry - Half angle??

cos(5[pi]/24)+cos([pi]/24)

i have to find the exact value of that.

so I simplified cos(5pi/24) to cos(pi/3 - pi/8) and then used a difference formula for cos to get
(sqrt2/2){[sqrt2+(sqrt2)]} + (sqrt3/2){[sqrt2-(sqrt2)]}

did the same thing for cos(pi/24) and got
(sqrt3/2){[sqrt2+(sqrt2)]} + (1/2){[sqrt2+(sqrt2)]}

so where do i go from there? How do I add these huge squarerooted expressions together to find the exact value? Please help. I'm running out of time and getting frustrated! Thank you!

anyone see what im doing wrong, if anything?


also... this homework assignment says to simplify without calculators:

Cos(85deg)sin(40deg)+sin(-5deg)sin(-50deg) - how do i go about doing that? do you think it is a typo where the sin(40deg) should be cos? cause that would make a lot more sense to me.