Ordinary Differential Equations Practice (Interactive)

Intuition

Equations that describe change: ODEs describe how things change, the speed of a falling object, the growth of a population, the oscillation of a spring. They are the language of physics, engineering, and biology.

Why it matters: Almost every physical law is expressed as a differential equation, Newton second law, Maxwell equations, Schrodinger equation. Solving ODEs lets you predict the future behaviour of physical systems.

The key insight: Most ODEs cannot be solved analytically, numerical methods (Euler, Runge-Kutta) approximate solutions, and the art is balancing accuracy against computational cost.

University Mathematics, Ordinary Differential Equations Practice

10 auto-graded practice problems at medium to hard difficulty. Select an answer, submit, and review the explanation.

First-Order ODEs

Second-Order Linear ODEs

Systems, Laplace Transforms, and Series Solutions

Common Mistakes

Using undetermined coefficients when the guess overlaps the complementary solution: When solving $y'' + y = 3\cos(x)$, the naive guess $A\cos(x) + B\sin(x)$ fails because $\cos(x)$ and $\sin(x)$ already appear in the complementary solution $y_c = C_1\cos(x) + C_2\sin(x)$. You must multiply the guess by $x$ (or $x^2$ for repeated roots) to obtain a linearly independent particular solution.

Confusing the integrating factor formula for first-order linear ODEs: For $y' + P(x)y = Q(x)$, the integrating factor is $\mu(x) = e^{\int P(x)\,dx}$, not $e^{\int Q(x)\,dx}$. The factor multiplies the entire equation to make the left side an exact derivative. Applying it to the wrong term gives an incorrect equation that cannot be integrated directly.

Forgetting the domain of validity for Laplace transforms: The Laplace transform $\mathcal{L}\{e^{at}\} = 1/(s-a)$ is only valid for $s > a$. When solving initial value problems, you must track the region of convergence to ensure the inverse transform is well-defined. Ignoring this can lead to incorrect solutions or missing terms.

Cross-References

• Site Home: Main landing page for Mathematics notes.
• Linear Algebra: Vector spaces, matrices, and linear transformations.
• Real Analysis: Rigorous treatment of real numbers and calculus.
• Practice: Practice problems for revision.