It is known that AB in semicircle o is the diameter ad = DC ∠ cab = 30 ° AC = 3 root sign 3, and the length of ad is calculated Don't use sin to solve the problem that we didn't learn

connect BC.BD Because angle DAB and angle DCB are two circular angles of the same chord (complementary) and ACB = 90 (circular angle of diameter) cab = 30. DAC = DCA (isosceles), so 2dac + BAC + ACB = 180. The solution is DAC = 30. Then it is compared with three sides of triangle ade

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