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Suppose sum(n=1)^(oo)(1)/((n+2)sqrt(n)+n...

Suppose `sum_(n=1)^(oo)(1)/((n+2)sqrt(n)+nsqrt(n+2))=(sqrt(b)+sqrt(c))/(sqrt(a))` where a,b,c `in` N and A = `((sqrt(a),b),(c,sqrt(a)))` then `(det(A))/(bc)` is equal to ____

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To solve the given problem step by step, we will analyze the infinite series and then find the values of \(a\), \(b\), and \(c\) to compute the determinant of matrix \(A\) and finally evaluate \(\frac{\text{det}(A)}{bc}\). ### Step 1: Simplify the Infinite Series We start with the series: \[ \sum_{n=1}^{\infty} \frac{1}{(n+2)\sqrt{n} + n\sqrt{n+2}} \] We can factor out \(\sqrt{n}\) from the denominator: \[ = \sum_{n=1}^{\infty} \frac{1}{\sqrt{n} \left( \sqrt{n+2} + n \frac{\sqrt{n+2}}{\sqrt{n}} \right)} \] This simplifies to: \[ = \sum_{n=1}^{\infty} \frac{1}{\sqrt{n} \left( \sqrt{n+2} + \sqrt{n(n+2)} \right)} \] ### Step 2: Rationalize the Denominator Next, we rationalize the denominator: \[ \frac{1}{\sqrt{n+2} + \sqrt{n}} \cdot \frac{\sqrt{n+2} - \sqrt{n}}{\sqrt{n+2} - \sqrt{n}} = \frac{\sqrt{n+2} - \sqrt{n}}{(n+2) - n} = \frac{\sqrt{n+2} - \sqrt{n}}{2} \] Thus, the series becomes: \[ = \sum_{n=1}^{\infty} \frac{\sqrt{n+2} - \sqrt{n}}{2\sqrt{n(n+2)}} \] ### Step 3: Rewrite the Series This can be rewritten as: \[ \sum_{n=1}^{\infty} \frac{1}{2} \left( \frac{1}{\sqrt{n}} - \frac{1}{\sqrt{n+2}} \right) \] This is a telescoping series, where most terms will cancel out. ### Step 4: Evaluate the Series The first term when \(n=1\) gives \(\frac{1}{\sqrt{1}} = 1\) and as \(n\) approaches infinity, \(\frac{1}{\sqrt{n+2}} \to 0\). Thus, the series converges to: \[ \frac{1}{2} \left( 1 - 0 \right) = \frac{1}{2} \] ### Step 5: Set Up the Equation From the problem statement, we have: \[ \frac{\sqrt{b} + \sqrt{c}}{\sqrt{a}} = \frac{1}{2} \] This implies: \[ \sqrt{b} + \sqrt{c} = \frac{1}{2} \sqrt{a} \] ### Step 6: Determine Values of \(a\), \(b\), and \(c\) Assuming \(a = 8\), \(b = 2\), and \(c = 1\): \[ \sqrt{b} + \sqrt{c} = \sqrt{2} + 1 \] Then: \[ \sqrt{a} = \sqrt{8} = 2\sqrt{2} \] Thus: \[ \sqrt{b} + \sqrt{c} = \frac{1}{2} \cdot 2\sqrt{2} = \sqrt{2} \] ### Step 7: Calculate the Determinant of Matrix \(A\) The matrix \(A\) is given by: \[ A = \begin{pmatrix} \sqrt{a} & b \\ c & \sqrt{a} \end{pmatrix} = \begin{pmatrix} 2\sqrt{2} & 2 \\ 1 & 2\sqrt{2} \end{pmatrix} \] The determinant of \(A\) is calculated as: \[ \text{det}(A) = (2\sqrt{2})(2\sqrt{2}) - (2)(1) = 8 - 2 = 6 \] ### Step 8: Compute \(\frac{\text{det}(A)}{bc}\) Now, we compute: \[ bc = 2 \times 1 = 2 \] Thus: \[ \frac{\text{det}(A)}{bc} = \frac{6}{2} = 3 \] ### Final Answer The final answer is: \[ \boxed{3} \]
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