The identity is .
(Apply sum of angles formula: )
(Substitute )
(Multiply)
(Simplify)
is an identity.
![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=10c8daeb86d0c964593b67463093f473.png\")
.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=149af8fb7ef5f985fff4f1f0ef6f1679.png\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=a43c750fa5f6f0992daddbd01c13a050.png\")
)![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=3565fd35149556022e3654b7d7274595.png\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=6247351ed8babe4910ac71b3b61c23a2.png\")
(Substitute ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=06e5bfa7e9863e46256e9c19747de7d2.png\")
)![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=3a1afe898b482db6a7f611df6425f394.png\")
(Multiply)![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=b524ccaa47a3d2221d506a33ae76b479.png\")
(Simplify)![\"\"](\"/userfiles/image/steps_images/solution.JPG\")
![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=10c8daeb86d0c964593b67463093f473.png\")
is an identity.