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{\bf Question}

Write down the differential operator ${\cal L}$ which enables the
following equation to be expressed as ${\cal L}[x(t)] = 0$: $\sin
t \frac{d^2x}{dx^2} + 3t\frac{dx}{dt} + \cos t \, x = 0$

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{\bf Answer}

$${\cal L} = \sin t \frac{d^2}{dx^2} + 3t\frac{d}{dt} + \cos t$$


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