I dont even know how to describe that... :S finding an exact value of cos36??
This one says: Noting that t=pi/5 satisfies 3t=pi-2t , fins the exact value of cos36.....This identities may be uself: cos^2t+sin^2t=1 , sin2t=2sintcost sin3t=3sint-4sin^3t Any clues???
Re: I dont even know how to describe that... :S finding an exact value of cos36??
Finding the exact value of is the same as finding the same value of , because .
You are given formulae for sin, so we're going to use them:
But we can also do this:
Since is the same no matter how we write it:
, that means we can simplify the relation by .
Let be , so .
PS: I think this thread should be here.