As shown in the figure, in RT △ AOB, ∠ B = 40 °, take OA as radius, O as center, make ⊙ o, intersect AB at point C, intersect ob at point D. calculate the degree of CD

Connect OC, ∵ o = 90 °, B = 40 °, a = 180-90-40 ° = 50 °, OA = OC, ∵ ACO = a = 50 °, COD = ACO - B = 10 ° and the degree of CD is 10 °

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1. As shown in the figure, it is known that point O is a point on the hypotenuse of RT △ ABC, with point o as the center and OA length as the radius, the center O and BC are tangent to point E As shown in the figure, we know that the point O is a point on the hypotenuse AC of ABC of RT triangle. With the point o as the center and the OA length as the radius, the center O and BC are tangent to point E and intersect with AC at point D, connecting AE. (1) proof: AE bisection angle CAC (2) explore the quantitative relationship between angle 1 and angle C in the figure Just ask the second question, the first question I know
2. As shown in the figure, in the known RT △ ABC, the ⊙ o cross bevel BC with ab as the diameter is at point D, and E is the midpoint of AC. connect ed and extend the extension line of intersection AB at point F. (1) prove that De is the tangent of ⊙ o; (2) if ⊙ f = 30 ° AB = 4, find the length of DF and ef
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11. As shown in the figure, in RT △ AOB, the circle AB with radius OA intersects at point C. If Ao = 5, OB = 12, the length of BC is obtained
12. In the R T triangle AOB, ∠ o = 90 degrees, OA = 6, OB = 8, take o as the center of the circle, OA as the radius, make the circle AB to C, and find the length of BC?
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14. As shown in the figure, OA, ob, OC are ⊙ o radius - AC = - BC, D, e are OA, ob, are the midpoint CD and CE equal? Why is it as shown in the figure
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16. As shown in the figure, it is known that in △ AOB, ∠ AOB = 90 ° OD ⊥ AB is at point D. the circle with point o as the center and OD as the radius intersects OA at point E, intercept BC = ob on Ba, and prove that CE is the tangent of ⊙ o
17. As shown in the figure, in the two concentric circles with o as the center, the chord AB and CD of the big circle are equal, and AB and the small circle are tangent at point E
18. As shown in the figure, the center of two concentric circles is O, the radius of big circle O is OA, OB intersects small circle O with C, D, please explain: AB / / CD I hope we don't use center angle and circle angle
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