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=5fd065470ba9bcb97d452df1296b14cc.png\")
.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=aceb01b513af137c9716022f5adcd04e.png\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=a43c750fa5f6f0992daddbd01c13a050.png\")
)![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=db71811033479b1396e56e6f541b0843.png\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=5d5c0200af4370aaac7e9b8819eb046b.png\")
(Substitute ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=ee4f7ad57a5a1f6e8b9335e532237b4f.png\")
)![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=4ca45afb134a4a425e1d16e41516e942.png\")
(Multiply)![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=c748471f96a297d892b9abf2aad893b9.png\")
(Simplify)![\"\"](\"/userfiles/image/steps_images/solution.JPG\")
![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=5fd065470ba9bcb97d452df1296b14cc.png\")
is an identity.