Question

uggggh:

using half-angle identities to evaluate cos(π/8) exactly...

I did cos(π/8) = cos (π/4/2) = +-√(1+cos(π/4)/2) = (-sin(π/4))/2....

Am I already wrong?

Answer 1

the question just asks to use half-angle identites to find the exact measure of cos(pi/8)

Answer 2

no what you doing is right

Answer 3

www.sosmath.com/trig/douangl/douangl.html
- tells u all about it there

Answer 4

so does sqr(1+cos(pi/4)) = -sin(pi/4) ?

Answer 5

Yeah just cos pi/4 = sqrt(2)/2

Answer 6

sqr(1+cos(pi/4)) is not equal to -sin(pi/4)

Answer 7

why you get involved the sinus you know the value of cosPI/4 put that in equation then reach the cosPI/8

Answer 8

the value of cos(pi/4) is not an exact measure tho

Answer 9

the value of cos(pi/8) isn't an exact measure either

Answer 10

right....but the question says to "use the half-angle identities to evaluate cos(pi/8) exactly"