# P5 hyperbolic identity help!!!!

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#1
Hey can someone please show me how to prove this identity...

cosh3A is identical to 3sinhA+4sinh^3 A

Help is much appreciated!
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15 years ago
#2
Sorry, you are wrong, should be sinh3A
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#3
sorry, i was typing it from the book and copied it down wrong. Could you show me how to do it please!
0
15 years ago
#4
Ok, sinh3A = 1/2(e^3A -e^-3A)
3sinhA + 4sinh^3 A = 3/2(e^A-e^-A) + 4/8 (e^A-e^-A)^3
then just use (a-b)^3 = a^3 - 3ba^2 + 3ab^2 - b^3...
Hope u can do it.
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