Subjects differential equations

Separation Variables

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Separation Variables


1. The problem asks which differential equations can be solved using the method of separation of variables. 2. Separation of variables works when the equation can be written as $$\frac{dy}{dx} = g(x)h(y)$$, meaning the right side is a product of a function of $x$ and a function of $y$. 3. Let's analyze each option: - A: $$\cos(x) \frac{dy}{dx} = \sin(x) \implies \frac{dy}{dx} = \frac{\sin(x)}{\cos(x)} = \tan(x)$$. This is $$\frac{dy}{dx} = g(x)$$ only, no $y$ term, so separable as $$\frac{dy}{dx} = g(x) \cdot 1$$. - B: $$\cos(x) \frac{dy}{dx} = \sin(y) \implies \frac{dy}{dx} = \frac{\sin(y)}{\cos(x)} = g(x)h(y)$$ with $$g(x) = \frac{1}{\cos(x)}$$ and $$h(y) = \sin(y)$$, separable. - C: $$\frac{dy}{dx} = e^{x+y} = e^x e^y$$, product of functions of $x$ and $y$, separable. - D: $$\frac{dy}{dx} = \ln(x + y)$$, cannot be separated into product of functions of $x$ and $y$ alone, not separable. - E: $$\frac{dy}{dx} = e^{2x} \tan(y)$$, product of functions of $x$ and $y$, separable. - F: $$\frac{dy}{dx} = e^{2y} \tan(y)$$, depends only on $y$, no $x$ term, so can be written as $$g(x)h(y)$$ with $$g(x) = 1$$, separable. 4. Therefore, equations A, B, C, E, and F are separable. Final answer: A, B, C, E, F