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