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The discussion addresses the mathematical proof of the identity $$\sinh \left( \tanh^{-1} (x) \right) = \frac{x}{ \sqrt{1-x^2}}$$. It begins by recalling the definition of the hyperbolic sine function and the inverse hyperbolic tangent function. The proof involves substituting the expression for $$\tanh^{-1}(x)$$ into the formula for $$\sinh$$ and simplifying the result. The final step confirms that the left-hand side equals the right-hand side, validating the identity. Additional questions can be directed to the specified math help forum.
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$$\sinh \left( \tanh^{-1} (x) \right) = \frac{x}{ \sqrt{1-x^2}}$$
 
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Hey Mohammed , We know that :$$\sinh(x) = \frac{e^{x}-e^{-x}}{2}$$

$$\sinh\left( \tanh^{-1} (x) \right) = \frac{e^{\tanh^{-1} (x)}-e^{-\tanh^{-1} (x)}}{2}$$

We know also :

$$\tanh^{-1} (x) = \ln \left( \sqrt{ \frac{1+x}{1-x}} \right)$$

$$\sinh \left( \tanh^{-1} (x) \right) = \frac{ \sqrt{ \frac{1+x}{1-x} }- \sqrt{ \frac{1-x}{1+x} } }{2}$$

$$\sinh \left( \tanh^{-1} (x) \right) = \frac{x}{ \sqrt{1-x^2}}$$

if you have further questions you can post them in the http://www.mathhelpboards.com/f10/section .
 
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