數學問題1條!~~~~~~~~~有圖!!!!!!!!!!!!10分~!!!

你係咪打錯左？
因為 ext.∠ of△既關係，
∠CAD無可能=∠BED
如果你既問題係
In the figure, AED and CDB are straight lines.∠CAD=∠BAD
and ∠CED=∠BED
就咁計：
1a)∠CEA=180°-∠CED(adj.∠on st. line)
∠BEA=180°-∠BED(adj.∠on st. line)
∵∠CED=∠BED(given)
∴∠CEA=∠BEA

∠ACE=180°-∠CEA-∠CAD(∠sum of △)
∠ABE=180°-∠BEA-∠BAD(∠sum of △)
∵∠CAD=∠BAD(given)
∴∠ACE=∠ABE
△AEC=△AEB(AAA)

1b)∵△AEC=△AEB(proved) and AED is a straight line
∴∠EDC=∠EDB
∠EDC+∠EDB=180°(adj.∠on st. line)
2∠EDC=180°
∠EDC=90°

1a.Prove triangle AEC is congruent to traingle AEB
似乎條式錯左
如(angle CAD = angle BED)根本冇關係
應該係angleCAD=angleBAD
可以咁計
because angleCAD=angleBAD
angle CED = angle BED
180-angleCED=angleAEC=180-angle BED=angleAEB
AE=AE(common side)
therefore triangle AEC is congruent to traingle AEB(A.S.A.)(Angle Side Angle)


1b.Show that angle EDC = 90度呢條可以咁計
because triangle AEC is congruent to traingle AEB,and CDB is a straight line
therefore angleCDA=angleADB
180/2=90
therefore angleEDC = 90