Question 730412
<pre>
15° is the difference between the two special angles 45° and 30°

We use the formula

cos(A-B) = cos(A)cos(B) + sin(A)sin(B)

where A = 45° and B = 30°  

cos(15°) = 

cos(45°-30°) = cos(45°)cos(30°) + sin(45°)sin(30°) = 

{{{(sqrt(2)/2)(sqrt(3)/2)}}} + {{{(sqrt(2)/2)(1/2)}}} = 

{{{sqrt(6)/4}}} + {{{sqrt(2)/4}}} = 

{{{(sqrt(6)+sqrt(2))/4}}}

Edwin</pre>