History of Hindu Mathematics: A Source Book v2.c17.s14.97

v2.c17.s14.97

Kṛṣṇa points out that it can also be found thus : $4Nm² = (m² + N)² - (m² ~ N)², identically.$ $∴ 4Nm² + (m² ~ N)² = (m² + N)²,$ or N(2m/(m²~ N))²+1=((m²+N)/(m²~ N))².