Question

如图,在四边形a b c d中a c平分角bad,b c等于dc,ce垂直于ad,c f垂直于ab bc垂足分别为e,f

Answer 1

因为平分角,所以∠EAC = ∠FAC,加上 ∠AEC = ∠AFC = 90,AC共线,因此△AEC = △AFC.

=》 CE = CF & AE = AF

因为 CE = CF,∠CED = ∠CFB = 90,CD = BC,所以△CDE = △CBF,因此 ED = BF

AD + DE = AF = AB - BF => 9 + DE = 21 - BF =》 DE = BF,所以 DE = 6