Direction Fields

Direction fields are a good way to visualize the solutions of a differential equation.

Since $\displaystyle\frac{dy}{dx} = f(x,y)$, at each point $\left(x_0,y_0\right)$ in the $xy$-plane we can draw a short line with slope $f\left(x_0,y_0\right)$. This is called a direction field. A solution to the differential equation $\displaystyle\frac{dy}{dx} = f(x,y)$ is then a curve that is everywhere tangent to the direction field.


Examples: The direction fields of $$\displaystyle\frac{dy}{dx} = x+y,\qquad \displaystyle\frac{dy}{dx} = 2x, \quad\text{ and } \quad \displaystyle\frac{dy}{dx}=y,$$ are (respectively)


The following video goes over the details and shows how to deduce information about the solutions of the corresponding differential equations.