As shown in the figure, ⊙ o, if the chord ad ∥ BC, Da = DC, ∠ AOC = 160 °, then ∠ BCO is equal to______ Degree

As shown in the figure, ⊙ o, if the chord ad ∥ BC, Da = DC, ∠ AOC = 160 °, then ∠ BCO is equal to______ Degree

Connect AC ∵ - B = 12 ∵ AOC = 80 ∵ - D = 180 ∵ - B = 100 ∵ ad = CD, OA = OC ∵ DAC = ∵ ACD = 40 degree, ∵ OCA = ∵ OAC = 10 ∵ ad ∥ BC ∵ ACB = ∵ DAC = 40 ∵ OCB = 30 degree

Let m be the middle point of the radius op of the spherical center O, passing through M and O respectively to make a plane perpendicular to OP, and two circles are obtained on the truncated surface, then the area ratio of the two circles is: ()
A. 14B. 12C. 23D. 34

Let the radius of the three circles be R1, R2, and R, then: R12 = R2 − (12R) 2 = 34r2, R22 = R2  R12: R22 = 34r2: R2 = 34, R2 = 34, the area ratio of the two circles is: 34, so D is selected

Let m be the middle point of the radius op of the spherical center O, passing through M and O respectively to make a plane perpendicular to OP, and two circles are obtained on the truncated surface, then the area ratio of the two circles is: ()
A. 14B. 12C. 23D. 34

Let the radius of the three circles be R1, R2, and R, then: R12 = R2 − (12R) 2 = 34r2, R22 = R2  R12: R22 = 34r2: R2 = 34, R2 = 34, the area ratio of the two circles is: 34, so D is selected

Let m and n be two points on the radius op of the ball center O, and NP = Mn = OM, respectively, through N, m and o as perpendicular lines, intercept the ball on the surface of OP to obtain three circles, then the area ratio of these three circles is: ()
A. 3，5，6B. 3，6，8C. 5，7，9D. 5，8，9

Let n, m, o be perpendicular to the surface of OP respectively, and the radius of the three circles be R1, R2, R3, and R, then: R12 = R2 − (23R) 2 = 59r2, R22 = R2 − (13R) 2 = 89r2, R32 = R2 − (23R) 2 = R2 ℅ R12: R22: R32 = 5:8:9 ℅ the area ratio of the three circles is 5, 8, 9, so D is selected