Find the exact value for the following cos 7pi12 Graph one c

Find the exact value for the following. cos 7pi/12 Graph one complete cycle. Label the accurately. y - sin pix

cos(7pi/12)

now 7pi/12 = 4pi/12 +3pi/12

cos(4pi/12 +3pi/12) = cos(pi/3 +pi/4)

use the formula : cos(A+B) =cosAcosB -sinAsinB

So, cos(pi/3 +pi/4) = cospi/3cospi/4 - sinpi/3sinpi/4

= (1/2)(1/sqrt2) - (sqrt3/2)(1/sqrt2)

= ( 1 - sqrt3)/2sqrt2

cos(7pi/12) = ( 1 - sqrt3)/2sqrt2