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Ajima Naonobu

Japanese Mathematician of the Edo Period

Ajima Naonobu (1732–1798) was a prominent mathematician of Japan’s Edo period, recognized for his groundbreaking work in geometry, infinite series, and integral methods. He was associated with the wazan (Japanese mathematics) tradition and carried forward the legacy of Seki Takakazu and Aida Yasuaki.

Ajima studied curves and areas, devising techniques that resembled integral calculus. He developed summation formulas and applied them to approximate areas under curves, paralleling developments in Europe by Newton and Leibniz, though his work evolved independently. In particular, he explored expansions of trigonometric functions and methods for handling series convergence.

He also applied mathematics to astronomy and mapmaking, reflecting the practical applications of his theoretical studies. His writings emphasized logical rigor and clarity, and he often communicated ideas through the traditional sangaku (mathematical tablets hung in Shinto shrines), where challenging problems were displayed for public engagement.

Ajima’s work demonstrated the global character of mathematical thought: despite Japan’s isolation, his methods showed striking parallels with Western calculus. He is remembered as one of the last great masters of wazan, symbolizing both the creativity and sophistication of Japanese mathematics before the full arrival of Western science in the Meiji era.