Which of the following exact differential equations have solutions?

I.$4x\sin y + \left( 2x^2\cos y + 8y \right) \frac{dy}{dx} = \cfrac1x$II.$xe^{x^2+y^2} + e^{x^2+y^2} \cfrac{dy}{dx} = 1$III.$\ln x + \sec^2 y \cfrac{dy}{dx} = 0$

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