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f(x) = lim(n->oo) sin^(2n)(pix)+[x+1/2],...

` f(x) = lim_(n->oo) sin^(2n)(pix)+[x+1/2]`, where [.] denotes the greatest integer function, is

A

continuous ar x=1 but discontinuous at x=3/2

B

cotinuous at x=1 but x=3//2

C

discontinuous at x= 1 and x= 3/2

D

c=discontinous at x=1 but continuous at =3/2

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to analyze the function given by: \[ f(x) = \lim_{n \to \infty} \sin^{2n}(\pi x) + \left[ x + \frac{1}{2} \right] \] where \([.]\) denotes the greatest integer function. We will check the continuity of \(f(x)\) at the points \(x = 1\) and \(x = \frac{3}{2}\). ### Step 1: Evaluate \(f(1)\) First, we calculate \(f(1)\): \[ f(1) = \lim_{n \to \infty} \sin^{2n}(\pi \cdot 1) + \left[ 1 + \frac{1}{2} \right] \] Since \(\sin(\pi) = 0\), we have: \[ \sin^{2n}(\pi) = 0 \quad \text{for any } n \geq 1 \] Thus, \[ f(1) = 0 + \left[ 1 + \frac{1}{2} \right] = 0 + [1.5] = 1 \] ### Step 2: Evaluate \(f(1 + h)\) Next, we consider \(f(1 + h)\) as \(h \to 0\): \[ f(1 + h) = \lim_{n \to \infty} \sin^{2n}(\pi(1 + h)) + \left[ (1 + h) + \frac{1}{2} \right] \] This simplifies to: \[ f(1 + h) = \lim_{n \to \infty} \sin^{2n}(\pi + \pi h) + \left[ 1 + h + \frac{1}{2} \right] \] Since \(\sin(\pi + \pi h) = -\sin(\pi h)\), we have: \[ \sin^{2n}(\pi + \pi h) = \sin^{2n}(\pi h) \] As \(h \to 0\), \(\sin(\pi h) \to \pi h\), and thus: \[ \sin^{2n}(\pi h) \to 0 \quad \text{(for } n \to \infty \text{)} \] Therefore, \[ f(1 + h) = 0 + \left[ 1 + h + \frac{1}{2} \right] = [1.5 + h] \] For \(h\) close to 0, \([1.5 + h] = 1\). ### Step 3: Evaluate \(f(1 - h)\) Now, we evaluate \(f(1 - h)\): \[ f(1 - h) = \lim_{n \to \infty} \sin^{2n}(\pi(1 - h)) + \left[ (1 - h) + \frac{1}{2} \right] \] This simplifies to: \[ f(1 - h) = \lim_{n \to \infty} \sin^{2n}(\pi - \pi h) + \left[ 1 - h + \frac{1}{2} \right] \] Again, since \(\sin(\pi - \pi h) = \sin(\pi h)\): \[ f(1 - h) = \lim_{n \to \infty} \sin^{2n}(\pi h) + [1.5 - h] \] As before, \(\sin^{2n}(\pi h) \to 0\) as \(h \to 0\): \[ f(1 - h) = 0 + [1.5 - h] \] For \(h\) close to 0, \([1.5 - h] = 1\). ### Step 4: Check Continuity at \(x = 1\) Now we check the continuity at \(x = 1\): \[ f(1) = 1, \quad f(1 + h) \to 1, \quad f(1 - h) \to 1 \text{ as } h \to 0 \] Since \(f(1) = f(1 + h) = f(1 - h)\), the function is continuous at \(x = 1\). ### Step 5: Evaluate \(f\left(\frac{3}{2}\right)\) Next, we evaluate \(f\left(\frac{3}{2}\right)\): \[ f\left(\frac{3}{2}\right) = \lim_{n \to \infty} \sin^{2n}\left(\pi \cdot \frac{3}{2}\right) + \left[ \frac{3}{2} + \frac{1}{2} \right] \] Since \(\sin\left(\frac{3\pi}{2}\right) = -1\): \[ \sin^{2n}\left(\frac{3\pi}{2}\right) = 1 \quad \text{(for any } n \geq 1\text{)} \] Thus, \[ f\left(\frac{3}{2}\right) = 1 + [2] = 1 + 2 = 3 \] ### Step 6: Evaluate \(f\left(\frac{3}{2} + h\right)\) Now, we consider \(f\left(\frac{3}{2} + h\right)\): \[ f\left(\frac{3}{2} + h\right) = \lim_{n \to \infty} \sin^{2n}\left(\pi\left(\frac{3}{2} + h\right)\right) + \left[ \frac{3}{2} + h + \frac{1}{2} \right] \] This simplifies to: \[ f\left(\frac{3}{2} + h\right) = \lim_{n \to \infty} \sin^{2n}\left(\frac{3\pi}{2} + \pi h\right) + \left[ 3 + h \right] \] Since \(\sin\left(\frac{3\pi}{2} + \pi h\right) = -\cos(\pi h)\): \[ f\left(\frac{3}{2} + h\right) = \lim_{n \to \infty} \sin^{2n}\left(-\cos(\pi h)\right) + [3 + h] \] As \(h \to 0\), \(-\cos(\pi h) \to -1\), thus: \[ \sin^{2n}(-\cos(\pi h)) \to 0 \quad \text{(for } n \to \infty\text{)} \] So, \[ f\left(\frac{3}{2} + h\right) = 0 + [3 + h] = 3 \] ### Step 7: Evaluate \(f\left(\frac{3}{2} - h\right)\) Now, we evaluate \(f\left(\frac{3}{2} - h\right)\): \[ f\left(\frac{3}{2} - h\right) = \lim_{n \to \infty} \sin^{2n}\left(\pi\left(\frac{3}{2} - h\right)\right) + \left[ \frac{3}{2} - h + \frac{1}{2} \right] \] This simplifies to: \[ f\left(\frac{3}{2} - h\right) = \lim_{n \to \infty} \sin^{2n}\left(\frac{3\pi}{2} - \pi h\right) + \left[ 3 - h \right] \] Since \(\sin\left(\frac{3\pi}{2} - \pi h\right) = -\cos(\pi h)\): \[ f\left(\frac{3}{2} - h\right) = \lim_{n \to \infty} \sin^{2n}(-\cos(\pi h)) + [3 - h] \] As \(h \to 0\), \(-\cos(\pi h) \to -1\), thus: \[ \sin^{2n}(-\cos(\pi h)) \to 0 \quad \text{(for } n \to \infty\text{)} \] So, \[ f\left(\frac{3}{2} - h\right) = 0 + [3 - h] = 2 \] ### Step 8: Check Continuity at \(x = \frac{3}{2}\) Now we check the continuity at \(x = \frac{3}{2}\): \[ f\left(\frac{3}{2}\right) = 3, \quad f\left(\frac{3}{2} + h\right) \to 3, \quad f\left(\frac{3}{2} - h\right) \to 2 \] Since \(f\left(\frac{3}{2} - h\right) \neq f\left(\frac{3}{2}\right)\), the function is discontinuous at \(x = \frac{3}{2}\). ### Conclusion The function \(f(x)\) is continuous at \(x = 1\) and discontinuous at \(x = \frac{3}{2}\). ### Final Answer The function \(f(x)\) is continuous at \(x = 1\) but discontinuous at \(x = \frac{3}{2}\). ---
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