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need solution for RD Sharma maths class 12 chapter Differentiation exercise 10.4 question 27

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Answer:

\frac{d y}{d x}=\frac{-e^{x}\left(e^{y}-1\right)}{e^{y}\left(e^{x}-1\right)}

Hint:

Use chain rule

Given:

e^{x}+e^{y}=e^{x+y}

Solution:

e^{x}+e^{y}=e^{x+y}

Differentiate w.r.t x

\frac{d}{d x}\left(e^{x}+e^{y}\right)=\frac{d\left(e^{x+y}\right)}{d x}

\frac{d\left(e^{x}\right)}{d x}+\frac{d\left(e^{y}\right)}{d x}=\frac{d\left(e^{x+y}\right)}{d(x+y)} \times \frac{d(x+y)}{d x}                        [Using chain rule]

e^{x}+\frac{d\left(e^{y}\right)}{d y} \times \frac{d y}{d x}=e^{x+y} \times\left(\frac{d x}{d x}+\frac{d y}{d x}\right)                    \left[\because \frac{d\left(e^{x}\right)}{d x}=e^{x}\right]

e^{x}+e^{y} \frac{d y}{d x}=e^{x+y}+e^{x+y} \frac{d y}{d x}

e^{y} \frac{d y}{d x}-e^{x+y} \frac{d y}{d x}=e^{x+y}-e^{x}

\frac{d y}{d x}\left(e^{y}-e^{x+y}\right)=\left(e^{x+y}-e^{x}\right)

\frac{d y}{d x}=\frac{e^{x+y}-e^{x}}{e^{y}-e^{x+y}}

\frac{d y}{d x}=\frac{e^{x} \cdot e^{y}-e^{x}}{e^{y}-e^{x} \cdot e^{y}}

       =\frac{e^{x}\left(e^{y}-1\right)}{e^{y}\left(1-e^{x}\right)}

       =\frac{e^{x}\left(e^{y}-1\right)}{e^{y}\left(-\left(e^{x}-1\right)\right)}

\frac{d y}{d x}=-\frac{e^{x}\left(e^{y}-1\right)}{e^{y}\left(e^{x}-1\right)}

Thus proved

 

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