Cuemath
Cuemath: Differential Equation
A comprehensive guide for learning all about differential equations with definitions, differential equation formulas, methods to solve them, their applications, solved examples, and practice questions.
University of St. Andrews (UK)
University of St. Andrews: Sofia Vasilyevna Kovalevskaya
This site provides a detailed biography of the famous mathematician, Sofia Vasilyevna Kovalevskaya (Sonja Kovalevsky). Includes six pictures and details of Kovalevskaya's (1850-1891 CE) life and works.