The trigonometric expression is .
Apply the sum-to-product formula : .
The simplified expression is .
![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=d82fc10a4693d9165717a506a72e166a.png\")
.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=33c81aece828d14ac0faadd6a18e79a3.png\")
.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=81c9e3325ea35f0e6719dddf78a34782.png\")
![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/solution.JPG\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=bf1da31df51b119097a648a9479052e8.png\")
.