Vedic Mathematics
Every chapter of Bhāratī Kṛṣṇa Tīrtha’s Vedic Mathematics (1965), animated step by step and then practised.
Each sūtra is a one-line Sanskrit aphorism that names a method: Ūrdhva-Tiryagbhyām, “vertically and crosswise”; Nikhilaṁ Navataścaramaṁ Daśataḥ, “all from nine and the last from ten”. Pick a lesson, either in the book’s chapter order or grouped by sūtra. Watch the digits move, try your own numbers, then practise. Tīrtha said the sūtras came from an appendix to the Atharvaveda. They don’t appear in any known text, and historians regard the system as his own. The panel beside each lesson shows the algebra that makes each method work either way.