The Double Cosine Integral - Solved Using Feynman Integration

Feynman Academy course: https://feynman-academy-course.vercel.app/#/join Chapters 1 and 2 are free. Chapter 3 and beyond start with a 7-day trial, then $10/month unless canceled. Subscribe: https://www.youtube.com/channel/UCepKxh_j0SH2cw0nbY9FwZQ?sub_confirmation=1 Course path (Jan 18, 2026 and newer) Lesson 18 of 32 Start here: https://youtu.be/8xq0RW1VurI Previous lesson: https://youtu.be/FjrS0KCLN1o Next lesson: https://youtu.be/_MtjcYp5ioA About this lesson: Learn how to use Richard Feynman's favorite math trick—differentiation under the integral sign—to crush impossible calculus problems. This step-by-step guide breaks down the Double Cosine Integral for beginners.