Proving the Relationship between tanh^-1(x) and ln((1+x)/(1-x))

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In summary, to prove that tanh-1(x) is equal to (1/2)ln((1+x)/(1-x)), the person rewrote it as ln(x+(x2+1)1/2)/ln(x+(x2-1)1/2). They then used the equation y=tanh(x)=sinh(x)/cosh(x)=(e^x-e^(-x))/(e^x+e^(-x)) and solved for u by setting u=e^x. This allowed them to successfully find the inverse function and solve the problem.
  • #1
harrietstowe
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Homework Statement


I need to prove that tanh-1(x) is equal to (1/2)ln((1+x)/(1-x))


Homework Equations





The Attempt at a Solution


I rewrote it as ln(x+(x2+1)1/2)/ln(x+(x2-1)1/2)

from here I am stuck. Thank you
 
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  • #2
harrietstowe said:

Homework Statement


I need to prove that tanh-1(x) is equal to (1/2)ln((1+x)/(1-x))


Homework Equations





The Attempt at a Solution


I rewrote it as ln(x+(x2+1)1/2)/ln(x+(x2-1)1/2)

from here I am stuck. Thank you

Start with y=tanh(x)=sinh(x)/cosh(x)=(e^x-e^(-x))/(e^x+e^(-x)). To find the inverse function you want to solve for x in terms of y, right? The trick is to put u=e^x, so e^(-x)=1/u. Solve for u first.
 
  • #3
Thanks so much, tried your way and worked out great
 

1. What is tanh^-1(x)?

Tanh^-1(x) is the inverse hyperbolic tangent function. It is the inverse of the hyperbolic tangent function, tanh(x), and is used to find the angle whose hyperbolic tangent is x.

2. How is tanh^-1(x) used in proofs?

Tanh^-1(x) is commonly used in trigonometric proofs involving hyperbolic functions. It allows for the manipulation and simplification of equations involving hyperbolic tangents.

3. What is the domain and range of tanh^-1(x)?

The domain of tanh^-1(x) is (-1,1), as it is the inverse of the hyperbolic tangent function whose range is (-1,1). The range of tanh^-1(x) is (-∞,∞).

4. How do you evaluate tanh^-1(x)?

To evaluate tanh^-1(x), we use the following formula: tanh^-1(x) = (1/2)ln[(1+x)/(1-x)]. This can also be rewritten as tanh^-1(x) = (1/2)[ln(1+x) - ln(1-x)]. This formula can be derived from the definition of the inverse hyperbolic tangent function.

5. What are some common identities involving tanh^-1(x)?

Some common identities involving tanh^-1(x) include: tanh^-1(-x) = -tanh^-1(x), tanh^-1(0) = 0, and tanh^-1(∞) = ∞. There are also various trigonometric identities that involve tanh^-1(x), such as the double angle formula and the addition/subtraction formula.

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