A triangle ABC has a cevian: a segment AD from vertex A to a point D on the opposite side BC. Drag A, B, or C to reshape the triangle, and drag D along side BC. The cevian splits BC into two segments, m from B to D and n from D to C. Stewart's theorem says b squared times m plus c squared times n equals a times the quantity d squared plus m times n, where a, b, c are the triangle's sides and d is the cevian length. The two sides of this equation are computed live and stay equal. An info button opens a drawer explaining Stewart's theorem.