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explain solution RD Sharma class 12 Chapter 18 Indefinite Integrals exercise 18.30 question 54

Answers (1)

Answer:

                \frac{1}{4} \log \left|\frac{x^{4}-1}{x^{4}}\right|+C

Hint:

            To solve this integration, we use partial fraction method   

Given:

            \int \frac{1}{x\left(x^{4}-1\right)} d x \\

Explanation:

Let

\begin{aligned} &I=\int \frac{1}{x\left(x^{4}-1\right)} d x \\ &I=\int \frac{x^{3}}{x^{4}\left(x^{4}-1\right)} d x \end{aligned}                 [Multiply and divide byx^{3}]

Let x^{4}=y

4x^{3}dx= dy

\begin{aligned} &I=\frac{1}{4} \int \frac{d y}{y(y-1)} \\ &I=\frac{1}{4} \int \frac{1+y-y}{y(y-1)} d y \\ &I=\frac{1}{4} \int \frac{y-(y-1)}{y(y-1)} d y \end{aligned}

\begin{aligned} &I=\frac{1}{4}\left[\int \frac{1}{y-1} d y+\int \frac{-1}{y} d y\right] \\ &I=\frac{1}{4}[\log |y-1|-\log |y|]+C \\ &I=\frac{1}{4} \log \left|\frac{y-1}{y}\right|+C \end{aligned}

As

\begin{aligned} &y=x^{4} \\ &I=\frac{1}{4} \log \left|\frac{x^{4}-1}{x^{4}}\right|+C \end{aligned}

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