Part 5/9:
The health of Euler took a drastic turn in his thirties when he lost his right eye to severe fevers. Despite the setback, his dedication to mathematics remained unwavering. He demonstrated remarkable resilience, continuing to produce groundbreaking work, notably in celestial mechanics and the study of the three-body problem while working in Berlin under King Frederick the Great. His formulation of exponential functions and the interrelation of trigonometry reached new heights, showcasing his ability to draw parallels between seemingly disparate realms of mathematics.