Defense Order (defense order)

And extends to the circumference, intersects the circle at point e,

Connect ce, de, ad and db.

∫ab is the diameter, ∴∠ACB=90? ，∠ADB=90？

∫CD segmentation ∠ACB

,∴∠ACD=∠BCD=45？

①∫∠ACD and ∠ABD

Is the circumferential angle on the same chord AD, ∴∠ACD=∠ABD=45? ,

∠∠BCD and ∠∠ ∠BAD.

Is the angle of the circle on the same string BD.

,∴∠BCD=∠BAD=45？

∴AD=BD

△ABD is an isosceles right triangle.

Point O is the center of the circle and the midpoint of AB.

, de split, ADB,

∠ADE=∠BDE=45？

∠∠CBA and ∠ADC.

Is the angle of a circle on the same chord AC.

,∴∠CBA=ADC= 15？

∴∠EDC=∠ADE-∠ADC=45？ - 15? =30?

,

∴cos(∠EDC)=cos30？ =√3/2=CD/ED

,

∴

CD = ED√3/2 = AB√3/2 = 2√3/2 = 3