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Explain solution RD Sharma class 12 chapter 19 Definite Integrals exercise Multiple choice question 45 maths

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Answer:

\frac{a}{2} \int_{0}^{a} f(x) d x

Hint:

To solve this equation we use  \int_{0}^{a} f(x) d x  formula.

Given:

f(x)=f(a-x), \quad g(x)+g(a-x)=a

Explanation:

\begin{aligned} &I=\int_{0}^{a} g(x) f(x) d x \ldots(i) \\\\ &\text { Put } x=(a-x) \\\\ &=\int_{0}^{a} g(a-x) f(a-x) d x \ldots(i i) \end{aligned}

\begin{aligned} &=\int_{0}^{a} f(x)(a-g(x)) d x \\\\ &I=a \int_{0}^{a} f(x) d x-\int_{0}^{a} f(x) \cdot g(x) d x \end{aligned}

\begin{gathered} I=a \int_{0}^{a} f(x) d x-I \\\\ 2 I=a \int_{0}^{a} f(x) d x \\\\ I=\frac{a}{2} \int_{0}^{a} f(x) d x \end{gathered}

 

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