Ab 2 = be 2+AE 2
Ac 2 = ce 2+AE 2
Ae 2 = ad 2-de 2
BD=CD
BE=BD+DE=CD+DE
CE=CD-DE
Ab 2+AC 2 = (CD+de) 2+(CD-de) 2+2 * (ad 2-de 2)
= 2 * CD 2+2 * de 2+2 * ad 2-2 * de 2
= 2 (광고 2+DC 2)