Skip to content
Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

algebra

Mental math with the difference of squares

taught

Using $(m+k)(m-k)=m^2-k^2$ in reverse to multiply or square two-digit numbers by hand.

Taught in

Requires

Required by

Nothing in the catalog needs this yet.