Question

Evaluate cos(31pi/3) I need help solving this, my notes suck.

Answer 1

0.8437

Answer 2

I think its a reference point or something. my answer sheet has 1/2 , -1/2, \[\sqrt{3}/2\], and -\[\sqrt{3/2}\]

Answer 3

\[31\pi/3=(30\pi+\pi)/3=5(2\pi)+\pi/3\]

Answer 4

This means your solution is the same as \[\cos \pi/3\]

Answer 5

Which should be pretty close to 1/2.

Answer 6

ok, I thought it was -1/2 , Is there an easier formula to do?

Answer 7

You need to remove all the multiples of \[2\pi\] that you can, then look at what you have left.

Answer 8

ok ok, because cos 60 is 1/2 and it's in Q1, so it's positive. Got it!

Answer 9

Well done.

Answer 10

Thanks so much.