Question

trigonometry finding exact identity value for cos 7pi/12?

Answer 1

it will be easier if we convert to degrees form, first
because pi=180 degrees
cos ( 7pi/12) = cos (7*180/12) = cos(105) deg
then, we know that 105 = 60+45, so
cos105 = cos(45+60)
now, use the formula :
cos (a+b) = cosa*cosb -sina*sinb

Answer 2

thankss!

Answer 3

yw