Q.

If f'xxfxfx+xfxxx2  dx  is equal to m  tan1fxxnx+c,  where m, n   R and ‘c’ is constant of integration (x > 0) then mn is equal to

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answer is 1.

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Detailed Solution

We are tasked with evaluating the integral:

∫ [f'(x) * (x - f(x)) / (f(x) + x) * (xfxx - x²)] dx    

and determining the ratio m/n, where the solution is expressed as:

I = m * tan⁻¹(f(x) - x) / n * x + c,    

where m and n are real numbers, and c is the constant of integration.

Step-by-Step Solution

  1. Rewrite the given integral in terms of its components:

    I = ∫ [f'(x) * (x - f(x)) / (xfxx)] dx            

  2. Simplify the terms to make substitution feasible:

    I = ∫ [f'(x) * (x - f(x)) / (xfxx²)] dx.            

  3. Let us substitute a new variable:

    Let t² = xfxx - x.                Therefore, f'(x) * (x - f(x)) / (xfxx²) dx = 2t dt.            

  4. Substitute the simplified terms back into the integral:

    I = ∫ [2t / (t² + 2t)] dt.            

  5. Integrate the simplified expression:

    I = 2 * tan⁻¹(t) + c.            

  6. Replace t with its original value in terms of xfxx:

    t = sqrt(xfxx - x).            

    Hence,

    I = 2 * tan⁻¹((f(x) - x) / x) + c.            

  7. Compare the final expression to the given form:

    I = m * tan⁻¹(f(x) - x) / n * x + c.            

    By comparison:

    m = 2, n = 2.            

Final Result

The ratio m/n is:

        m/n = 2/2 = 1.    

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