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Find \( \iint_{R} \frac{x y^{2}}{x^{2}+1} d A, R=[0,2] \times[-3,3] \) Round your answer to four decimal places.

Ask by Bowman Christensen. in the United States
Mar 12,2025

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The value of the double integral is approximately 14.4849.

Solución

We start with the double integral \[ \iint_R \frac{x y^2}{x^2 + 1}\, dA, \] where the region is \[ R = [0,2] \times [-3,3]. \] ### Step 1. Write the integral as an iterated integral Since the region is rectangular, the integral can be written as \[ \int_{x=0}^{2} \int_{y=-3}^{3} \frac{x y^2}{x^2+1} \,dy\,dx. \] ### Step 2. Evaluate the inner integral (with respect to \( y \)) For a fixed \( x \), the integrand is \[ \frac{x y^2}{x^2+1}, \] where \( \frac{x}{x^2+1} \) is a constant in terms of \( y \). Thus, we have \[ \int_{y=-3}^{3} \frac{x y^2}{x^2+1} dy = \frac{x}{x^2+1} \int_{y=-3}^{3} y^2\,dy. \] Notice that \( y^2 \) is an even function. Therefore, \[ \int_{y=-3}^{3} y^2\,dy = 2\int_{0}^{3} y^2\,dy. \] Compute the integral: \[ \int_{0}^{3} y^2\,dy = \left[\frac{y^3}{3}\right]_{0}^{3} = \frac{27}{3} = 9. \] Thus, \[ \int_{y=-3}^{3} y^2\,dy = 2 \times 9 = 18. \] So the inner integral becomes \[ \frac{x}{x^2+1} \times 18 = \frac{18x}{x^2+1}. \] ### Step 3. Evaluate the outer integral (with respect to \( x \)) Now we need to compute \[ \int_{x=0}^{2} \frac{18x}{x^2+1}\,dx. \] Factor out the constant: \[ 18 \int_{0}^{2} \frac{x}{x^2+1}\,dx. \] ### Step 4. Use substitution for the \( x \)-integral Let \[ u = x^2+1 \quad \text{so that} \quad du = 2x\,dx. \] Then, \[ \frac{du}{2} = x\,dx. \] Change the limits: - When \( x = 0 \), \( u = 0^2+1 = 1 \). - When \( x = 2 \), \( u = 2^2+1 = 5 \). Substitute into the integral: \[ 18 \int_{u=1}^{5} \frac{1}{u}\cdot\frac{du}{2} = 18 \cdot \frac{1}{2} \int_{1}^{5} \frac{du}{u} = 9 \int_{1}^{5} \frac{du}{u}. \] ### Step 5. Compute the logarithmic integral The integral is \[ \int_{1}^{5} \frac{du}{u} = \ln|u|\Big|_{1}^{5} = \ln(5) - \ln(1). \] Since \( \ln(1) = 0 \), we have \[ \int_{1}^{5} \frac{du}{u} = \ln(5). \] Thus, the overall value becomes \[ 9\ln(5). \] ### Step 6. Final answer The value of the given double integral is \[ 9\ln(5) \approx 14.4849, \] rounded to four decimal places.

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To solve the double integral \( \iint_{R} \frac{x y^{2}}{x^{2}+1} \, dA \) over the region \( R = [0,2] \times [-3,3] \), we can express it in terms of iterated integrals: \[ \iint_{R} \frac{x y^{2}}{x^{2}+1} \, dA = \int_{0}^{2} \int_{-3}^{3} \frac{x y^{2}}{x^{2}+1} \, dy \, dx. \] Let's first evaluate the inner integral: \[ \int_{-3}^{3} \frac{x y^{2}}{x^{2}+1} \, dy. \] Since \( \frac{x}{x^2+1} \) is constant with respect to \( y \), we can factor it out: \[ = \frac{x}{x^2 + 1} \int_{-3}^{3} y^{2} \, dy. \] Next, we calculate \( \int_{-3}^{3} y^{2} \, dy \): \[ \int_{-3}^{3} y^{2} \, dy = \left[ \frac{y^3}{3} \right]_{-3}^{3} = \frac{3^3}{3} - \frac{(-3)^3}{3} = \frac{27}{3} - \frac{-27}{3} = 9 + 9 = 18. \] Now substitute this back into the integral: \[ \int_{-3}^{3} \frac{x y^{2}}{x^{2}+1} \, dy = \frac{x}{x^{2} + 1} \cdot 18 = \frac{18x}{x^{2}+1}. \] Now substitute this result into the outer integral: \[ \int_{0}^{2} \frac{18x}{x^{2}+1} \, dx. \] To evaluate this integral, we can use the substitution \( u = x^2 + 1 \), so \( du = 2x \, dx \) or \( dx = \frac{du}{2x} \). When \( x = 0 \), \( u = 1\), and when \( x = 2\), \( u = 5\): \[ \int_{0}^{2} \frac{18x}{x^{2}+1} \, dx = 18 \cdot \int_{1}^{5} \frac{1}{u} \cdot \frac{du}{2} = 9 \int_{1}^{5} \frac{du}{u}. \] Evaluating the integral \( \int \frac{du}{u} \): \[ 9 \int_{1}^{5} \frac{du}{u} = 9 \left[ \ln |u| \right]_{1}^{5} = 9 (\ln 5 - \ln 1) = 9 \ln 5. \] Calculating \( \ln 5 \): Using the approximation \( \ln 5 \approx 1.6094 \): \[ 9 \ln 5 \approx 9 \cdot 1.6094 = 14.4846. \] Now, rounding to four decimal places, we get: \[ \boxed{14.4846}. \]

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