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6.2 Integrable first-order differential equations

We begin by considering differential equations of the form:

dydx=f(x)\frac{dy}{dx}=f(x)

where f(x)f(x) is a function of xx. A solution to this equation is given by y=F(x)y=F(x), where F(x)F(x) is a function with F(x)=f(x)F^{\prime}(x)=f(x). By the fundamental theorem of calculus, we can obtain F(x)F(x) by integrating f(x)f(x). Differential equations of this form are called integrable.

Example.

Solve the differential equation dydx=1x-2\frac{dy}{dx}=\frac{1}{x-2}.

Solution. We integrate 1/(x-2)1/(x-2) to get y=log|x-2|+cy={\log|x-2|}+c where cc is a constant.