Question 1142797
<pre>
Note that  {{{ cos(72^o) = (1/4)((sqrt(5)) - 1)  }}}


RHS:  {{{ (2cos(72^o))^2 = (2((1/4)((sqrt(5)) - 1)))^2 }}}
 = {{{ (1/4)(5) - (2/4)(sqrt(5)) + (1/4) }}}
 = {{{  (3/2) - (1/2)sqrt(5) }}}

LHS:   {{{ 1 - 2cos(72^o) =  1 - 2 ((1/4)((sqrt(5)) - 1))  }}} 
 = {{{ 1 - (1/2)(sqrt(5) - 1) }}}
 = {{{ (3/2) - (1/2)(sqrt(5)) }}}