# Slope fields

1. Apr 13, 2014

### Jhenrique

I know that the standard definition for a slope field is $\frac{dy}{dx} = f(x, y)$, but and if the equation given is a second-order ODE $a\frac{d^2y}{dx^2}+b\frac{dy}{dx}+cy=0$ or a system of first-order ODEs $A\frac{d\vec{r}}{dt}+\vec{b}=\vec{0}$, the definition for slope field continues the same? I need only isolate dy/dx and thus the slope field is automatically generated?

2. Apr 13, 2014

### HallsofIvy

Staff Emeritus
Given a second order differential equation, you would write it as two first order differential equations:
$z= dy/dx$ and $adz/dx+ bz+ cy= 0$.

Now, if your $\vec{r}$ has greater dimension than 1 you "slope field" would have to have greater dimensions also. With the single variable y as a function of t, your "slope field" is a two dimension graph with axes y and t, so can be drawn on a sheet of paper. If you have variables x, y as part of your vector function, your "slope field" is a three dimension graph with axes x, y, and t. If you have variables x, y, as part of your vector function, your slope field is a four dimension graph with axes x, y, z, and t. If you succeed in drawing such a thing, please post it here!