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For a,b∈Ra, b \in R and a<ba < b, ∫abf(x)f(x)+f(a+b−x) dx=\int_{a}^{b} \frac{f(x)}{f(x) + f(a + b - x)} \, dx =

Solution

✅ Correct Option: 4

Let I=∫abf(x)f(x)+f(a+b−x) dxI = \int_{a}^{b} \frac{f(x)}{f(x) + f(a+b-x)} \, dx.

Using property ∫abg(x) dx=∫abg(a+b−x) dx\int_{a}^{b} g(x) \, dx = \int_{a}^{b} g(a+b-x) \, dx:

I=∫abf(a+b−x)f(a+b−x)+f(x) dxI = \int_{a}^{b} \frac{f(a+b-x)}{f(a+b-x) + f(x)} \, dx.

Adding: 2I=∫ab1 dx=b−a2I = \int_{a}^{b} 1 \, dx = b - a.

So I=b−a2I = \frac{b-a}{2}.

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