I have one more that has me stumped. In verifying the following identity,

I came up with a form that was close to the desired form, but ........

Well you know what they say about getting close. I rechecked by algebra and it all looks good. Help!

sinh 3x = 3sinh x + 4 (sinh^3) x

NOTE: In case its not clear the last term is 4 times sinh cubed x, where the sinh function is cubed.