Question 1137318
.
<pre>
Apply the formula for the sine of the arguments' difference 


sin(a-b) = sin(a)*cos(b) - cos(a)*sin(b).


You will get


{{{sin(4pi/9)cos(pi/9) - cos(4pi/9)sin(pi/9)}}} = {{{sin(4pi/9-pi/9)}}} = {{{sin(3pi/9)}}} = {{{sin(pi/3)}}} = {{{sqrt(3)/2}}}.
</pre>


Solved, answered and completed.