Contact us
Choose a category below so we can get back to you as quickly as possible.
取CD的中點F,連接EF EF是梯形ABCD的中位線,所以有:EF=(AD+BC)/2=CD/2=CF=DF 因為EF=CF,有角FEC=角FCE 因為EF=DF,有角FED=角FDE 所以: 角DEC=角DEF+角CEF=(角DEF+角CEF+角FDE+角FCE)/2=180/2=90 是直角. 所以DE垂直EC
We and our partners use cookies and other technologies to analyze traffic and optimize your experience. View more info and control your cookies settings at any time in our Cookies Policy.