证明:
做AE垂直于BC于E,则有
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(AD^2+DC^2)
证明:
做AE垂直于BC于E,则有
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(AD^2+DC^2)