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If ∫dx(x−1)3/4.(x+2)5/4=α[1−g(x)]β+c\int \frac{dx}{(x-1)^3/^4. (x+2)^5/^4} = \alpha[1 - g(x)]^\beta + c, where cc is a constant of integration, then which of the following are true?

(A) α=23\alpha = \frac{2}{3}

(B) β=34\beta = \frac{3}{4}

(C) 3α+4β=53\alpha + 4\beta = 5

(D) g(x)=3(x+2)g(x) = \frac{3}{(x+2)}

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 4

We need to evaluate:

I=∫dx(x−1)3/4 (x+2)5/4I = \int \frac{dx}{(x-1)^{3/4}\,(x+2)^{5/4}}

The total power in the denominator is 34+54=2\frac{3}{4} + \frac{5}{4} = 2, so we substitute:

t=x−1x+2t = \frac{x-1}{x+2}


dt=(x+2)(1)−(x−1)(1)(x+2)2 dxdt = \frac{(x+2)(1) - (x-1)(1)}{(x+2)^2}\,dx

=3(x+2)2 dx= \frac{3}{(x+2)^2}\,dx

dx=(x+2)23 dtdx = \frac{(x+2)^2}{3}\,dt


Since x−1=t(x+2)x - 1 = t(x+2), we get (x−1)3/4=t3/4(x+2)3/4(x-1)^{3/4} = t^{3/4}(x+2)^{3/4}

The denominator becomes:

t3/4(x+2)3/4⋅(x+2)5/4=t3/4(x+2)2t^{3/4}(x+2)^{3/4} \cdot (x+2)^{5/4} = t^{3/4}(x+2)^{2}


I=∫(x+2)2/3t3/4 (x+2)2 dtI = \int \frac{(x+2)^2/3}{t^{3/4}\,(x+2)^{2}}\,dt

=13∫t−3/4 dt= \frac{1}{3}\int t^{-3/4}\,dt

=13⋅t1/41/4+c= \frac{1}{3} \cdot \frac{t^{1/4}}{1/4} + c

=43 t1/4+c= \frac{4}{3}\,t^{1/4} + c


I=43(x−1x+2)1/4+cI = \frac{4}{3}\left(\frac{x-1}{x+2}\right)^{1/4} + c

x−1x+2=(x+2)−3x+2=1−3x+2\frac{x-1}{x+2} = \frac{(x+2)-3}{x+2} = 1 - \frac{3}{x+2}

I=43(1−3x+2)1/4+cI = \frac{4}{3}\left(1 - \frac{3}{x+2}\right)^{1/4} + c


Comparing with α [1−g(x)]β+c\alpha\,[1 - g(x)]^{\beta} + c:

α=43\alpha = \frac{4}{3}, β=14\quad \beta = \frac{1}{4}, g(x)=3x+2\quad g(x) = \frac{3}{x+2}


(A) α=23\alpha = \frac{2}{3} → α=43≠23\alpha = \frac{4}{3} \neq \frac{2}{3} ❌

(B) β=34\beta = \frac{3}{4} → β=14≠34\beta = \frac{1}{4} \neq \frac{3}{4} ❌

(C) 3α+4β=3×43+4×143\alpha + 4\beta = 3 \times \frac{4}{3} + 4 \times \frac{1}{4}

=4+1=5= 4 + 1 = 5 ✅

(D) g(x)=3x+2g(x) = \frac{3}{x+2} ✅


The correct answer is (C) and (D) only.

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