Question 1017962

Find the exact value by using a half-angle identity. 

cosine of five pi divided by twelve.
<pre>{{{cos (1/2)A = " "+- sqrt((1 + cos (A))/2)}}}
{{{cos ((5pi)/12)))}}}, or {{{cos (1/2)((5pi)/6)}}} = +{{{sqrt((1 + cos ((5pi)/6))/2)}}} = {{{sqrt((1 + (- sqrt(3)/2))/2)}}} = {{{sqrt((1 - sqrt(3)/2)/2)}}} = {{{sqrt((2/2 - sqrt(3)/2)/2)}}} = {{{sqrt(((2 - sqrt(3))/2)/2))}}} = {{{sqrt((2 - sqrt(3))/4))}}} = {{{highlight(highlight_green(highlight(sqrt(2 - sqrt(3))/2)))}}}