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If I=∫xx−x2−4dx=αx3+β(x2−4)32+γI = \int \frac{x}{x - \sqrt{x^2 - 4}} dx = \alpha x^3 + \beta(x^2 - 4)^{\frac{3}{2}} + \gamma, where γ\gamma is constant of integration, then

Solution

✅ Correct Option: 3

Multiply both numerator and denominator by (x+x2−4)(x + \sqrt{x^2 - 4}):

I=∫xx−x2−4⋅x+x2−4x+x2−4dxI = \int \frac{x}{x - \sqrt{x^2 - 4}} \cdot \frac{x + \sqrt{x^2 - 4}}{x + \sqrt{x^2 - 4}} dx


The denominator simplifies to:

(x−x2−4)(x+x2−4)(x - \sqrt{x^2 - 4})(x + \sqrt{x^2 - 4})

=x2−(x2−4)= x^2 - (x^2 - 4)

=4= 4

The numerator becomes x(x+x2−4)x(x + \sqrt{x^2 - 4})


The integral simplifies to:

I=∫x(x+x2−4)4dxI = \int \frac{x(x + \sqrt{x^2 - 4})}{4} dx

=14∫[x2+xx2−4]dx= \frac{1}{4} \int [x^2 + x\sqrt{x^2 - 4}] dx

=14∫x2dx+14∫xx2−4dx= \frac{1}{4} \int x^2 dx + \frac{1}{4} \int x\sqrt{x^2 - 4} dx


The first integral:

∫x2dx=x33\int x^2 dx = \frac{x^3}{3}


For the second integral, substitute u=x2−4u = x^2 - 4, so x dx=du2x \, dx = \frac{du}{2}:

∫xx2−4dx=∫u⋅du2\int x\sqrt{x^2 - 4} dx = \int \sqrt{u} \cdot \frac{du}{2}

=12∫u1/2du= \frac{1}{2} \int u^{1/2} du

=12⋅u3/23/2= \frac{1}{2} \cdot \frac{u^{3/2}}{3/2}

=13u3/2= \frac{1}{3}u^{3/2}

=13(x2−4)3/2= \frac{1}{3}(x^2 - 4)^{3/2}


Combining both integrals:

I=14⋅x33+14⋅13(x2−4)3/2+γI = \frac{1}{4} \cdot \frac{x^3}{3} + \frac{1}{4} \cdot \frac{1}{3}(x^2 - 4)^{3/2} + \gamma

=112x3+112(x2−4)3/2+γ= \frac{1}{12}x^3 + \frac{1}{12}(x^2 - 4)^{3/2} + \gamma


Comparing with the given form I=αx3+β(x2−4)32+γI = \alpha x^3 + \beta(x^2 - 4)^{\frac{3}{2}} + \gamma:

α=112\alpha = \frac{1}{12}

β=112\beta = \frac{1}{12}

Therefore, α=β\alpha = \beta

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