Carry out the following steps to show that $\int csch\ x\ dx = ln\left|tanh\frac{x}{2}\right| + C$. a) Change variables with the substitution $u = \frac{x}{2}$ to show that $\int csch\ x\ dx = \int \frac{2\ du}{sinh\ 2u}$. b) Use the identity $sinh\ 2u = 2sinh\ u\ cosh\ u$ to show that $\frac{2}{sinh\ 2u} = \frac{sech^2 u}{tanh\ u}$. c) Change variables again to determine $\int \frac{sech^2 u}{tanh\ u} du$. d) Express your answer in terms of x.
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Then $$du = \frac{1}{2} dx$$, so $$dx = 2du$$. Show more…
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Carry out the following steps to derive the formula $\left.\int \operatorname{csch} x \, d x=\ln |\tanh (x / 2)|+C \text { (Theorem } 6.9\right)$ a. Change variables with the substitution $u=x / 2$ to show that $$\int \operatorname{csch} x \, d x=\int \frac{2 d u}{\sinh 2 u}$$ b. Use the identity for sinh $2 u$ to show that $\frac{2}{\sinh 2 u}=\frac{\operatorname{sech}^{2} u}{\tanh u}$ c. Change variables again to determine $\int \frac{\operatorname{sech}^{2} u}{\tanh u} d u,$ and then express your answer in terms of $x$
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(a) Derive the identity $$ \frac{\operatorname{sech}^{2} x}{1+\tanh ^{2} x}=\operatorname{sech} 2 x $$ (b) Use the result in part (a) to evaluate $\int \operatorname{sech} x d x$. (c) Derive the identity $$ \operatorname{sech} x=\frac{2 e^{x}}{e^{2 x}+1} $$ (d) Use the result in part (c) to evaluate $\int \operatorname{sech} x d x$ (e) Explain why your answers to parts (b) and (d) are consistent.
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