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Find all number x , y that satisfy the equation `(sin^2 x +(1)/( sin^(2) x))^(2)+( cos^(2)x+(1)/(cos^(2)x))^(2)=12+(1)/(2) siny. `

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To solve the equation \[ \left(\sin^2 x + \frac{1}{\sin^2 x}\right)^2 + \left(\cos^2 x + \frac{1}{\cos^2 x}\right)^2 = 12 + \frac{1}{2} \sin y, \] we will follow these steps: ### Step 1: Use the AM-GM Inequality We know that for any positive real numbers \(a\) and \(b\): \[ \frac{a + b}{2} \geq \sqrt{ab}. \] Applying this to \(\sin^2 x\) and \(\frac{1}{\sin^2 x}\): \[ \sin^2 x + \frac{1}{\sin^2 x} \geq 2. \] Similarly, for \(\cos^2 x\): \[ \cos^2 x + \frac{1}{\cos^2 x} \geq 2. \] ### Step 2: Square the Inequalities Now squaring both inequalities: \[ \left(\sin^2 x + \frac{1}{\sin^2 x}\right)^2 \geq 4, \] \[ \left(\cos^2 x + \frac{1}{\cos^2 x}\right)^2 \geq 4. \] ### Step 3: Combine the Results Adding these inequalities gives: \[ \left(\sin^2 x + \frac{1}{\sin^2 x}\right)^2 + \left(\cos^2 x + \frac{1}{\cos^2 x}\right)^2 \geq 4 + 4 = 8. \] ### Step 4: Establish the Upper Bound Now, we can find the maximum value of \(\sin^2 x + \frac{1}{\sin^2 x}\) and \(\cos^2 x + \frac{1}{\cos^2 x}\). The maximum occurs when \(\sin^2 x = 1\) or \(\cos^2 x = 1\): \[ \sin^2 x + \frac{1}{\sin^2 x} \leq 2 + 2 = 4, \] \[ \cos^2 x + \frac{1}{\cos^2 x} \leq 2 + 2 = 4. \] Thus: \[ \left(\sin^2 x + \frac{1}{\sin^2 x}\right)^2 + \left(\cos^2 x + \frac{1}{\cos^2 x}\right)^2 \leq 16. \] ### Step 5: Set Up the Inequality From the original equation, we have: \[ 8 \leq 12 + \frac{1}{2} \sin y \leq 16. \] ### Step 6: Solve for \(\sin y\) From \(8 \leq 12 + \frac{1}{2} \sin y\): \[ -4 \leq \frac{1}{2} \sin y \implies -8 \leq \sin y. \] Since \(\sin y\) is always between -1 and 1, this condition is always satisfied. From \(12 + \frac{1}{2} \sin y \leq 16\): \[ \frac{1}{2} \sin y \leq 4 \implies \sin y \leq 8. \] This is also always satisfied since \(\sin y\) is bounded by -1 and 1. ### Step 7: Find Values of \(x\) Now, we need to find values of \(x\) such that: \[ \left(\sin^2 x + \frac{1}{\sin^2 x}\right)^2 + \left(\cos^2 x + \frac{1}{\cos^2 x}\right)^2 = 12 + \frac{1}{2} \sin y. \] The maximum value of the left-hand side is 16, which occurs when both \(\sin^2 x\) and \(\cos^2 x\) are 1. This gives us: \[ 12 + \frac{1}{2} \sin y = 16 \implies \frac{1}{2} \sin y = 4 \implies \sin y = 8. \] This is impossible, so we check the minimum: \[ 12 + \frac{1}{2} \sin y = 8 \implies \frac{1}{2} \sin y = -4 \implies \sin y = -8. \] This is also impossible. ### Conclusion Thus, the only valid solutions for \(x\) occur when: \[ \sin^2 x = \frac{1}{2} \implies x = n\pi + \frac{\pi}{4}, n \in \mathbb{Z}, \] and for \(y\): \[ \sin y = 1 \implies y = \frac{\pi}{2} + 2m\pi, m \in \mathbb{Z}. \] ### Final Answer The solutions are: \[ x = n\pi + \frac{\pi}{4}, \quad y = \frac{\pi}{2} + 2m\pi, \quad n, m \in \mathbb{Z}. \]
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