Question

Find an exact value cos(19pi/12)

Answer 1

ok... this is a 2nd quadrant problem so cos is negative

and you need the sum of 2 angles formula

\[\cos(\frac{19\pi}{12}) = \cos(\frac{5\pi}{6} + \frac{3\pi}{4})\]

so you need to find the 2 exact value triangles \[\cos(\frac{5\pi}{6}) = - \cos(\frac{\pi}{6})\]

\[\cos(\frac{3\pi}{4}) = - \cos(\frac{\pi}{4})\]

you will also need to find

\[\sin(\frac{5\pi}{6}) = \sin(\frac{\pi}{6})....and....\sin(\frac{3\pi}{4}) = \sin(\frac{\pi}{4})\]

hope this helps

Answer 2

is the answer sqrt 6 - sqrt 2 all over 4?

Answer 3

I haven't done the calculation

Answer 4

yep... thats the answer I got

Answer 5

okay thank you!