Logarithmic and Implicit Differentiation

Solve for \displaystyle \frac{dy}{dx}.

  1. y=\displaystyle \sqrt[5]{\frac{4^{x}\coth\left(e^{-x}\right)}{\sin\left(x^{2}\ln x\right)}}
  2. \displaystyle e^{y}=\cosh\left(e^{x}+\log_{3}y\right)-2^{{\displaystyle x^{2}}}

Solution

If we proceed directly in number 1, we get

\displaystyle \frac{dy}{dx}=\frac{ y^{-4}}{5}\cdot\frac{\sin\left(x^{2}\ln x\right)\cdot\left[4^{x}e^{-x}\mathrm{csch}^{2}\left(e^{-x}\right)+4^{x}\ln4\coth\left(e^{-x}\right)\right]}{\sin^{2}\left(x^{2}\ln x\right)}

\displaystyle \rule{0.0001em}{0.0001ex} \phantom{\frac{dy}{dx}=} -\frac{y^{-4}}{5}\cdot\frac{4^{x}\coth\left( e^{-x} \right)\cos\left(x^{2}\ln x\right)\left[ x+2x\ln x\right]}{\sin^{2}\left(x^{2}\ln x\right)}

Meanwhile, if we first simplify the expression by exploiting the properties of logarithms, we obtain

\displaystyle \ln y = \frac{1}{5} \left[ x\ln4 + \ln\coth \left( e^{-x}\right) - \ln \sin \left( x^{2}\ln x \right) \right]

from which the derivative is easier to compute compared to the previous:

\displaystyle \frac{dy}{dx}=\frac{1}{5}y\left[\ln4+\frac{e^{-x}\mathrm{csch}^{2}\left(e^{-x}\right)}{\coth\left(e^{-x}\right)}-\frac{\cos\left(x^{2}\ln x\right)\left[x+2x\ln x\right]}{\sin\left(x^{2}\ln x\right)}\right].

In number 2, we just differentiate the equation implicitly with respect to x:

\displaystyle e^{y} \frac{dy}{dx} = \sinh\left( e^{x} + \log_{3} y \right) \cdot \left(e^{x} + \frac{1}{y\ln 3} \frac{dy}{dx} \right) - 2x \ln 2 \cdot 2^{x^2}

Solving for \displaystyle \frac{dy}{dx}, we get

\displaystyle \frac{dy}{dx}=\frac{e^{x}\sinh\left(e^{x}+\log_{3}y\right)-2x \ln 2 \cdot2^{x^{2}}}{e^{y}-\dfrac{\sinh\left(e^{x}+\log_{3}y\right)}{y\ln3}}

\displaystyle \rule{0.0001em}{0.0001ex} \phantom{\frac{dy}{dx}} =\frac{y\ln3\left[e^{x}\sinh\left(e^{x}+\log_{3}y\right)-2x \ln 2 \cdot2^{x^{2}}\right]}{ye^{y}\ln3-\sinh\left(e^{x}+\log_{3}y\right)}.

One Response to “Logarithmic and Implicit Differentiation”

  1. paolo Says:

    sir kulang po ata ng ln2 yung number 2.

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