Question

Find an exact value. cos(pi/12)

Answer 1

i think we can use

cos 2x = 2cos^2x - 1

cos (pi/6) = 2 cos^ (pi/12) - 1

cos pi/6 = sqrt3/2

Answer 2

they want you to use the half angle formula \[\cos \frac{ x }{ 2 }= \pm \sqrt{\frac{ 1+cosx }{ 2 }}\]

Answer 3

oh ok
well just plug cos x ( in this case cos pi/6) into the firmula and work it out

Answer 4

when I do I don't get the right answer

Answer 5

The answer options are (sqrt6+sqrt2)/4 (-sqrt6+sqrt2)/4 (sqrt6-sqrt2)/4 (-sqrt6-sqrt2)/4

Answer 6

yes its an awkward one to work out

Answer 7

How would you work it out?

Answer 8

= sqrt [( 1 + sqrt3/2)/ 2]

Answer 9

How do you get from that to one of the answers? I dont understand how you get a sqrt 6 out of any of that

Answer 10

i simplified that to (1/2)( sqrt(2 + sqrt3))

Answer 11

i agree I think those answers are wrong.

Answer 12

because if you go on the calculator cos pi/12 = 0.9659
and my answers comes to the same value

Answer 13

oh hold on (sqrt6+sqrt2)/4 comes to 0.9659 as well

so that one is right

Answer 14

- also the negative of that is another solution

Answer 15

I'm not sure how they got to that ...