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Let $$\int \frac{2-\tan x}{3+\tan x} \mathrm{~d} x=\frac{1}{2}\left(\alpha x+\log _e|\beta \sin x+\gamma \cos x|\right)+C$$, where $$C$$ is the constant of integration. Then $$\alpha+\frac{\gamma}{\beta}$$ is equal to :

JEE · Math · previous-year question

  1. A.3
  2. B.7
  3. C.1
  4. D.4correct

Answer

D. 4

Explanation

$$I=\int \frac{2-\tan x}{3+\tan x} d x=\int \frac{2 \cos x-\sin x}{3 \cos x+\sin x} d x$$ Put, $$2 \cos x-\sin x=a(-3 \sin x+\cos x)+ b(3 \cos x+\sin x)$$ $$\begin{aligned} & a+3 b=2 \quad \text{.... (i)}\\ & -3 a+b=-1 \quad \text{.... (ii)} \end{aligned}$$ From equation (i) and (ii) $$a=b=\frac{1}{2}$$ $$I=\frac{1}{2} \int \frac{-3 \sin x+\cos x}{3 \cos x+\sin x} d x+\frac{1}{2} \int \frac{3 \cos x+\sin x}{3 \cos x+\sin x} d x$$ $$I=\frac{1}{2} \ln |3 \cos x+\sin x|+\frac{1}{2} x= \frac{1}{2}(d x+\log |\beta \sin x+\gamma \cos x|)$$ On comparing, we get $$I=\frac{1}{2} \ln |3 \cos x+\sin x|+\frac{1}{2} x=\frac{1}{2}(d x+\log |\beta \sin x+\gamma \cos x|)$$ On comparing, we get $$\begin{aligned} & \Rightarrow \frac{1}{2}(x+\log (|3 \cos x+\sin x|))= \\ & \qquad \frac{1}{2}(d x+\log |\beta \sin x+\gamma \cos x|) \end{aligned}$$ $$\begin{aligned} & \alpha=1, \beta=1, \gamma=3 \\ & \alpha+\frac{\gamma}{\beta}=1+\frac{3}{1}=4 \end{aligned}$$

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