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The solution of the equation (dy)/(dx) =...

The solution of the equation `(dy)/(dx) =(y^(2)-y-2)/(x^(2)+2x-3)` is

A

`(1)/(3)log|(y-2)/(y+1)|=(1)/(4)log|(x-1)/(x+3)|+c`

B

`(1)/(3)log|(y+1)/(y-2)|=(1)/(4)log|(x+3)/(x-1)|+c`

C

`(1)/(4)log|(y+1)/(y-2)| =(1)/(3) log|(x+3)/(x-1)|+c`

D

None of these

Text Solution

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The correct Answer is:
To solve the differential equation \[ \frac{dy}{dx} = \frac{y^2 - y - 2}{x^2 + 2x - 3}, \] we will use the method of separation of variables. ### Step 1: Factor the numerator and denominator First, we need to factor both the numerator and the denominator. **Numerator:** \[ y^2 - y - 2 = (y - 2)(y + 1). \] **Denominator:** \[ x^2 + 2x - 3 = (x + 3)(x - 1). \] So, we can rewrite the equation as: \[ \frac{dy}{dx} = \frac{(y - 2)(y + 1)}{(x + 3)(x - 1)}. \] ### Step 2: Separate the variables Now, we can separate the variables: \[ \frac{dy}{(y - 2)(y + 1)} = \frac{dx}{(x + 3)(x - 1)}. \] ### Step 3: Integrate both sides Next, we integrate both sides. We will perform partial fraction decomposition on both sides. **Left Side:** For \(\frac{1}{(y - 2)(y + 1)}\), we can write: \[ \frac{1}{(y - 2)(y + 1)} = \frac{A}{y - 2} + \frac{B}{y + 1}. \] Multiplying through by the denominator \((y - 2)(y + 1)\) gives: \[ 1 = A(y + 1) + B(y - 2). \] Setting \(y = 2\): \[ 1 = A(2 + 1) \implies A = \frac{1}{3}. \] Setting \(y = -1\): \[ 1 = B(-1 - 2) \implies B = -\frac{1}{3}. \] Thus, we have: \[ \frac{1}{(y - 2)(y + 1)} = \frac{1/3}{y - 2} - \frac{1/3}{y + 1}. \] Integrating gives: \[ \int \left( \frac{1/3}{y - 2} - \frac{1/3}{y + 1} \right) dy = \frac{1}{3} \ln |y - 2| - \frac{1}{3} \ln |y + 1| + C_1. \] **Right Side:** For \(\frac{1}{(x + 3)(x - 1)}\), we can write: \[ \frac{1}{(x + 3)(x - 1)} = \frac{C}{x + 3} + \frac{D}{x - 1}. \] Multiplying through by the denominator gives: \[ 1 = C(x - 1) + D(x + 3). \] Setting \(x = -3\): \[ 1 = D(-3 + 3) \implies D = \frac{1}{4}. \] Setting \(x = 1\): \[ 1 = C(1 - 1) + D(1 + 3) \implies C = \frac{1}{4}. \] Thus, we have: \[ \frac{1}{(x + 3)(x - 1)} = \frac{1/4}{x + 3} - \frac{1/4}{x - 1}. \] Integrating gives: \[ \int \left( \frac{1/4}{x + 3} - \frac{1/4}{x - 1} \right) dx = \frac{1}{4} \ln |x + 3| - \frac{1}{4} \ln |x - 1| + C_2. \] ### Step 4: Combine the results Setting the integrals equal to each other gives: \[ \frac{1}{3} \ln |y - 2| - \frac{1}{3} \ln |y + 1| = \frac{1}{4} \ln |x + 3| - \frac{1}{4} \ln |x - 1| + C. \] ### Step 5: Simplify This can be simplified to: \[ \ln \left( \frac{|y - 2|^{1/3}}{|y + 1|^{1/3}} \right) = \ln \left( \frac{|x + 3|^{1/4}}{|x - 1|^{1/4}} \right) + C. \] Exponentiating both sides gives: \[ \frac{|y - 2|^{1/3}}{|y + 1|^{1/3}} = K \cdot \frac{|x + 3|^{1/4}}{|x - 1|^{1/4}}, \] where \(K = e^C\). ### Final Result Thus, the general solution of the differential equation is: \[ \frac{|y - 2|^{1/3}}{|y + 1|^{1/3}} = K \cdot \frac{|x + 3|^{1/4}}{|x - 1|^{1/4}}. \]
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