Question 824322
<pre>
2cosē(6)

We use the identity 

cos(2<font face="symbol">q</font>) = 2cosē(<font face="symbol">q</font>)-1

We substitute 6 for <font face="symbol">q</font>

cos(2·6) = 2cosē(6)-1

cos(12) = 2cosē(6)-1

Add 1 to both sides:

1+cos(12) = 2cosē(6)

Edwin</pre>