The identity is .
Consider left hand side identity : .
The hyporbolic trigonometric function : .
= Right hand side identity.
.
![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=7be69ec2b5d44eb7fadd1f73ef7d9ad0.png\")
.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=8cba43800f8546c5d3e6a49487a72bfd.png\")
.![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=c36191d20ef937fac5e2e8cb9b368808.png\")
.![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=4ec0a2185d0671eb49d020a0d50fb8c0.png\")
![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/solution.JPG\")
![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=7be69ec2b5d44eb7fadd1f73ef7d9ad0.png\")
.