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Soit \(y \in \left]-\frac \pi2, \frac \pi2\right[\). On pose \(x = \ln\biggl(\tan\Bigl( \frac y2 + \frac \pi4\Bigr) \biggr)\).
Montrer que \(\tanh \frac x2 = \tan \frac y2\), \(\tanh x = \sin y\),\(\ch x = \frac 1{\cos y}\).
Soit \(y \in \left]-\frac \pi2, \frac \pi2\right[\). On pose \(x = \ln\biggl(\tan\Bigl( \frac y2 + \frac \pi4\Bigr) \biggr)\).
Montrer que \(\tanh \frac x2 = \tan \frac y2\), \(\tanh x = \sin y\),\(\ch x = \frac 1{\cos y}\).