# Math Help - hyberbolic manipulations

1. ## hyberbolic manipulations

how do you show that if x = ln ( tan ( y)) then tanh x = - cos ( 2y)?

2. Originally Posted by alexandrabel90
how do you show that if x = ln ( tan ( y)) then tanh x = - cos ( 2y)?
Start by observing that:

$x=\ln(\tan(y))$

mean that:

$e^x=\tan(y)$

then use the definition of the hyperbolic functions in terms of the exponential function to proceed.

CB