Evaluate the integral. \[ \int_{1}^{2} \frac{4 y^{2}-2 y-12}{y(y+2)(y-3)} d y \]
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To evaluate the integral \[ \int_{1}^{2} \frac{4 y^{2}-2 y-12}{y(y+2)(y-3)} \, dy, \] we can start by performing partial fraction decomposition on the integrand. We want to express \[ \frac{4 y^{2}-2 y-12}{y(y+2)(y-3)} \] in the form \[ \frac{A}{y} + \frac{B}{y+2} + \frac{C}{y-3}. \] Multiplying through by the common denominator \(y(y+2)(y-3)\) gives us \[ 4y^2 - 2y - 12 = A(y+2)(y-3) + B(y)(y-3) + C(y)(y+2). \] Expanding each term on the right-hand side: 1. \( A(y+2)(y-3) = A(y^2 - y - 6) = Ay^2 + (2A - 3A)y - 6A = Ay^2 + (2A - 3A)y - 6A \) 2. \( B(y)(y-3) = By^2 - 3By \) 3. \( C(y)(y+2) = Cy^2 + 2Cy \) Combining all terms yields: \[ (A + B + C)y^2 + (2A - 3B + 2C)y - 6A = 4y^2 - 2y - 12. \] Now, we equate coefficients: - For \(y^2\): \(A + B + C = 4\) - For \(y\): \(2A - 3B + 2C = -2\) - Constant: \(-6A = -12\) or \(A = 2\) Plugging \(A = 2\) into the other equations gives: 1. \(2 + B + C = 4 \implies B + C = 2\) 2. \(2(2) - 3B + 2C = -2 \implies 4 - 3B + 2C = -2 \implies 2C - 3B = -6\) Now we solve the equations: From \(B + C = 2\), we can express \(C\) as \(C = 2 - B\). Substitute this into \(2C - 3B = -6\): \[ 2(2 - B) - 3B = -6 \implies 4 - 2B - 3B = -6 \implies -5B = -10 \implies B = 2. \] Thus, \(C = 2 - 2 = 0\). We have: \[ A = 2, \quad B = 2, \quad C = 0. \] Therefore, we can rewrite our integrand as: \[ \frac{4y^2 - 2y - 12}{y(y+2)(y-3)} = \frac{2}{y} + \frac{2}{y+2}. \] Now, we can rewrite the original integral: \[ \int_{1}^{2} \left( \frac{2}{y} + \frac{2}{y+2} \right) dy. \] Now we evaluate this: \[ \int_{1}^{2} \frac{2}{y} \, dy + \int_{1}^{2} \frac{2}{y+2} \, dy. \] 1. For the first integral: \[ \int \frac{2}{y} \, dy = 2 \ln |y| \Big|_{1}^{2} = 2 (\ln 2 - \ln 1) = 2 \ln 2. \] 2. For the second integral, use the substitution \(u = y + 2\): \[ \int \frac{2}{y+2} \, dy = 2 \ln |y+2| \Big|_{1}^{2} = 2 (\ln 4 - \ln 3) = 2\ln\left(\frac{4}{3}\right). \] Putting it all together gives: \[ 2 \ln 2 + 2 \ln \left(\frac{4}{3}\right) = 2 \left(\ln 2 + \ln \left(\frac{4}{3}\right)\right) = 2 \ln \left(\frac{8}{3}\right). \] Thus,
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