Question

Find the exact value of the trig function:
cos(-2π/3)

Answer 1

You must remember that
\[\cos(\pi/3)=1/2\\
\sin(\pi/3)=\sqrt{3}/2\]
and use,
\[\cos(2\pi/3)=\cos^2(\pi/3)-\sin^2(\pi/3)\]
Could you continue from this point?

Answer 2

I wish :O no, please help further... :/

Answer 3

\[\cos(a) = \cos(-a)\]

Answer 4

So, cos(-2π/3) is the same thing as cos(2π/3)?

Answer 5

correct

Answer 6

So then it would be -1/2 ...? :)

Answer 7

correct

Answer 8

okay that makes much more sense! Thanks : )

Answer 9

who should I give the medal to? you both helped really well ...

Answer 10

the other guy

Answer 11

ok Lol