Prove that $mathrm{arcsinh}(x)$ is an odd function











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The inverse hyperbolic sine $sin^{-1}(x) = mathrm{arcsinh}(x)$ is an odd function. This can be proved by manipulating the expression $mathrm{arcsinh}(-x) = y$ as shown here.



But how to prove it through this definition instead?



$$mathrm{arcsinh}(x) = log left( x + sqrt{x^2 + 1} right)$$



My attempt:



I applied this rule, so obtaining



$$mathrm{arcsinh}(-x) = log left( sqrt{x^2 + 1} right) + log left( 1 - frac{x}{sqrt{x^2 + 1}} right)$$



This does not seem the expression of $mathrm{arcsinh}(x)$ with opposite sign. How to proceed?










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  • 2




    $(x+sqrt{x^2+1})(-x+sqrt{x^2+1})=1$
    – Lord Shark the Unknown
    Nov 24 at 14:37






  • 2




    The rule pulls you away from the solution, don't use it.
    – Yves Daoust
    Nov 24 at 14:39















up vote
0
down vote

favorite












The inverse hyperbolic sine $sin^{-1}(x) = mathrm{arcsinh}(x)$ is an odd function. This can be proved by manipulating the expression $mathrm{arcsinh}(-x) = y$ as shown here.



But how to prove it through this definition instead?



$$mathrm{arcsinh}(x) = log left( x + sqrt{x^2 + 1} right)$$



My attempt:



I applied this rule, so obtaining



$$mathrm{arcsinh}(-x) = log left( sqrt{x^2 + 1} right) + log left( 1 - frac{x}{sqrt{x^2 + 1}} right)$$



This does not seem the expression of $mathrm{arcsinh}(x)$ with opposite sign. How to proceed?










share|cite|improve this question


















  • 2




    $(x+sqrt{x^2+1})(-x+sqrt{x^2+1})=1$
    – Lord Shark the Unknown
    Nov 24 at 14:37






  • 2




    The rule pulls you away from the solution, don't use it.
    – Yves Daoust
    Nov 24 at 14:39













up vote
0
down vote

favorite









up vote
0
down vote

favorite











The inverse hyperbolic sine $sin^{-1}(x) = mathrm{arcsinh}(x)$ is an odd function. This can be proved by manipulating the expression $mathrm{arcsinh}(-x) = y$ as shown here.



But how to prove it through this definition instead?



$$mathrm{arcsinh}(x) = log left( x + sqrt{x^2 + 1} right)$$



My attempt:



I applied this rule, so obtaining



$$mathrm{arcsinh}(-x) = log left( sqrt{x^2 + 1} right) + log left( 1 - frac{x}{sqrt{x^2 + 1}} right)$$



This does not seem the expression of $mathrm{arcsinh}(x)$ with opposite sign. How to proceed?










share|cite|improve this question













The inverse hyperbolic sine $sin^{-1}(x) = mathrm{arcsinh}(x)$ is an odd function. This can be proved by manipulating the expression $mathrm{arcsinh}(-x) = y$ as shown here.



But how to prove it through this definition instead?



$$mathrm{arcsinh}(x) = log left( x + sqrt{x^2 + 1} right)$$



My attempt:



I applied this rule, so obtaining



$$mathrm{arcsinh}(-x) = log left( sqrt{x^2 + 1} right) + log left( 1 - frac{x}{sqrt{x^2 + 1}} right)$$



This does not seem the expression of $mathrm{arcsinh}(x)$ with opposite sign. How to proceed?







calculus real-analysis logarithms hyperbolic-functions






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asked Nov 24 at 14:34









BowPark

549720




549720








  • 2




    $(x+sqrt{x^2+1})(-x+sqrt{x^2+1})=1$
    – Lord Shark the Unknown
    Nov 24 at 14:37






  • 2




    The rule pulls you away from the solution, don't use it.
    – Yves Daoust
    Nov 24 at 14:39














  • 2




    $(x+sqrt{x^2+1})(-x+sqrt{x^2+1})=1$
    – Lord Shark the Unknown
    Nov 24 at 14:37






  • 2




    The rule pulls you away from the solution, don't use it.
    – Yves Daoust
    Nov 24 at 14:39








2




2




$(x+sqrt{x^2+1})(-x+sqrt{x^2+1})=1$
– Lord Shark the Unknown
Nov 24 at 14:37




$(x+sqrt{x^2+1})(-x+sqrt{x^2+1})=1$
– Lord Shark the Unknown
Nov 24 at 14:37




2




2




The rule pulls you away from the solution, don't use it.
– Yves Daoust
Nov 24 at 14:39




The rule pulls you away from the solution, don't use it.
– Yves Daoust
Nov 24 at 14:39










1 Answer
1






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6
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accepted










$$text{arsinh}(x)+text{arsinh}(-x)=log(sqrt{x^2+1}+x)+log(sqrt{x^2+1}-x)=log(x^2+1-x^2).$$



You can conclude.






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    1 Answer
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    active

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    1 Answer
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    active

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    active

    oldest

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    active

    oldest

    votes








    up vote
    6
    down vote



    accepted










    $$text{arsinh}(x)+text{arsinh}(-x)=log(sqrt{x^2+1}+x)+log(sqrt{x^2+1}-x)=log(x^2+1-x^2).$$



    You can conclude.






    share|cite|improve this answer

























      up vote
      6
      down vote



      accepted










      $$text{arsinh}(x)+text{arsinh}(-x)=log(sqrt{x^2+1}+x)+log(sqrt{x^2+1}-x)=log(x^2+1-x^2).$$



      You can conclude.






      share|cite|improve this answer























        up vote
        6
        down vote



        accepted







        up vote
        6
        down vote



        accepted






        $$text{arsinh}(x)+text{arsinh}(-x)=log(sqrt{x^2+1}+x)+log(sqrt{x^2+1}-x)=log(x^2+1-x^2).$$



        You can conclude.






        share|cite|improve this answer












        $$text{arsinh}(x)+text{arsinh}(-x)=log(sqrt{x^2+1}+x)+log(sqrt{x^2+1}-x)=log(x^2+1-x^2).$$



        You can conclude.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Nov 24 at 14:38









        Yves Daoust

        122k668218




        122k668218






























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