# Change of variables

## Contents

 Educational level: this is a tertiary (university) resource.
 Resource type: this resource is a lesson.
 Subject classification: this is a mathematics resource .
 Completion status: this resource is ~25% complete.

School:Mathematics > Topic:Differential_Equations > Ordinary Differential Equations > Change of Variables

### Definition

In a differential equation, if a certain term appears many different times, a substitution can be made similar to a $u$-substitution.

### Solution

1. Substitute a term for a variable (e.g. $\textstyle u=\frac {2y}{x}$).
2. Implicitly differentiate the variable (e.g. $\textstyle \frac {du}{dx}=\frac {2}{x} \frac {dy}{dx}$).
3. Solve for the derivative that needs to be solved (e.g. $\textstyle \frac {dy}{dx}=\frac {x}{2} \frac {du}{dx}$).
4. Solve the original equation in terms of $u$ and then use the substitution for $u$ to get the original equation back in terms of $x$ and $y$.