\
The expression is
.
\
Apply difference formula :
.
\
\
.
\
\
The trigonometric function is
.
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.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=6c29c04ac4043ae2affbb872c7e42a76.png\")
.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=76c6ad37f474d60d618a2aa352c05314.png\")
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.![\"\"](\"/userfiles/image/steps_images/solution.JPG\")
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.