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Use integral tables to evaluate the integral. \[ \int \frac{\sqrt{64-x^{2}}}{x} d x \]

Ask by Frank Love. in the United States
Jan 23,2025

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Answer

The integral evaluates to: \[ \sqrt{64 - x^{2}} - 8 \ln\left(\frac{8 + \sqrt{64 - x^{2}}}{x}\right) + C \]

Solution

To evaluate the integral \[ \int \frac{\sqrt{64 - x^{2}}}{x} \, dx, \] we can use a trigonometric substitution. Here's a step-by-step solution: ### Step 1: Trigonometric Substitution Let \( x = 8 \sin \theta \). Then: \[ dx = 8 \cos \theta \, d\theta, \] and \[ \sqrt{64 - x^2} = \sqrt{64 - 64 \sin^2 \theta} = 8 \cos \theta. \] ### Step 2: Substitute into the Integral Substituting \( x = 8 \sin \theta \) and \( dx = 8 \cos \theta \, d\theta \) into the integral: \[ \int \frac{8 \cos \theta}{8 \sin \theta} \cdot 8 \cos \theta \, d\theta = \int \frac{\cos \theta}{\sin \theta} \cdot 8 \cos \theta \, d\theta = 8 \int \frac{\cos^2 \theta}{\sin \theta} \, d\theta. \] ### Step 3: Simplify the Integrand Using the identity \( \cos^2 \theta = 1 - \sin^2 \theta \): \[ 8 \int \frac{1 - \sin^2 \theta}{\sin \theta} \, d\theta = 8 \left( \int \csc \theta \, d\theta - \int \sin \theta \, d\theta \right). \] ### Step 4: Integrate We know: \[ \int \csc \theta \, d\theta = -\ln \left| \csc \theta + \cot \theta \right| + C, \] and \[ \int \sin \theta \, d\theta = -\cos \theta + C. \] Thus, \[ 8 \left( -\ln \left| \csc \theta + \cot \theta \right| + \cos \theta \right) + C. \] ### Step 5: Back-Substitute \( \theta \) in Terms of \( x \) Recall that: \[ \sin \theta = \frac{x}{8}, \quad \cos \theta = \frac{\sqrt{64 - x^2}}{8}. \] So, \[ \csc \theta = \frac{8}{x}, \quad \cot \theta = \frac{\sqrt{64 - x^2}}{x}. \] Substituting these back into the expression: \[ -8 \ln \left| \frac{8 + \sqrt{64 - x^2}}{x} \right| + \sqrt{64 - x^2} + C. \] ### Final Answer Combining all the steps, the integral evaluates to: \[ \boxed{\,\sqrt{64 - x^{2}} \; -\; 8\,\ln\left(\frac{8 + \sqrt{64 - x^{2}}}{\,x\,}\right) + C\,} \]

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To evaluate the integral \(\int \frac{\sqrt{64-x^{2}}}{x} \, dx\), we can use a trigonometric substitution. Since we have \(\sqrt{64 - x^2}\), we can let \(x = 8\sin(\theta)\). This implies \(dx = 8\cos(\theta) \, d\theta\) and \(\sqrt{64 - x^2} = \sqrt{64(1 - \sin^2(\theta))} = 8\cos(\theta)\). Now we can transform the integral: \[ \int \frac{\sqrt{64-x^{2}}}{x} \, dx = \int \frac{8\cos(\theta)}{8\sin(\theta)} \cdot (8\cos(\theta) \, d\theta) = \int \frac{8\cos^2(\theta)}{\sin(\theta)} \, d\theta = 8 \int \frac{\cos^2(\theta)}{\sin(\theta)} \, d\theta. \] We can rewrite \(\cos^2(\theta)\) as \(\frac{1 - \sin^2(\theta)}{2}\): \[ 8 \int \frac{\cos^2(\theta)}{\sin(\theta)} \, d\theta = 8 \int \frac{1 - \sin^2(\theta)}{2\sin(\theta)} \, d\theta = 4 \int \frac{1}{\sin(\theta)} \, d\theta - 4 \int \sin(\theta) \, d\theta. \] The first integral is: \[ 4 \int \csc(\theta) \, d\theta = 4 \ln | \csc(\theta) - \cot(\theta) | + C, \] and the second integral is: \[ -4 (-\cos(\theta)) = 4\cos(\theta). \] Putting it all together, we have: \[ 4 \ln | \csc(\theta) - \cot(\theta) | + 4\cos(\theta) + C. \] Now we need to convert everything back in terms of \(x\). We have: \(\sin(\theta) = \frac{x}{8}\) and \(\cos(\theta) = \sqrt{1 - \left(\frac{x}{8}\right)^2} = \frac{\sqrt{64 - x^2}}{8}\). Also, \(\csc(\theta) = \frac{1}{\sin(\theta)} = \frac{8}{x}\) and \(\cot(\theta) = \frac{\cos(\theta)}{\sin(\theta)} = \frac{\sqrt{64 - x^2}}{x}\). Thus, the expression becomes: \[ \int \frac{\sqrt{64-x^{2}}}{x} \, dx = 4 \ln \left| \frac{8}{x} - \frac{\sqrt{64-x^2}}{x} \right| + \sqrt{64 - x^2} + C. \] This simplifies to: \[ \int \frac{\sqrt{64-x^{2}}}{x} \, dx = 4 \ln \left| \frac{8 - \sqrt{64-x^2}}{x} \right| + \sqrt{64 - x^2} + C. \]

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