a0a再黎7題!!加油－飛行里程

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a0a再黎7題!!加油

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a0a再黎7題!!加油 [IMG]http://i164.photobucket.com/albums/u4/ming21ki/IMG_0004-16.jpg[/IMG]

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(43) log 10x = -1 10x = 1/10 x = 1/100 (44) log 9/log 3 = 2 log 3/log 3 = 2 (45) The inequality is: 1500 × 1.6t > 3 × 105 1.6t > 200 t log 1.6 > log 200 t > 11.27 t = 12 (46) ∠BOA = 96° (Angle at centre = Twice of angle at circumference) △BOA is an isos. triangle So θ = (180° - 96°)/2 = 42° (47) Join DO where O is the centre of the circle, then ∠DOA = 76° (Angle at centre = Twice of angle at circumference) ∠DOB = 2x + 30° (Angle at centre = Twice of angle at circumference) So 2x + 30° + 76° = 180° 2x = 74° x = 37° (48) ∠ABC = 75° (Opp. angles of cyclic quad.) x = 180° - 48° - 75° = 57° (49) Join BC, then ∠BAD = ∠BCD : ∠ABC = ∠ADC = 2 : 3 (Arc ratio = angle ratio) Let ∠BAD = 2x, then ∠ADC = 3x and so 2x + 25° = 3x x = 25° So ∠BAD = 50°

其他解答:

43 ：log 10x = -1 10x = 10^(-1) = 1/10 所以 x = 1/100 44 ：log9 / log3 = log(3^2) / log3 = 2log3 / log3 = 2 45 ：n > 3x10^5 i.e. 1500x 1.6^t > 3x10^5 1.6^t > 200 t log 1.6 > log 200 t > 11.3 46 ：角AOB= 2(48) = 96 度所以 θ = 0.5 ( 180 - 96 ) = 42 度 47 ：角DBA = 38度 , 角ADB = 90度 so , x + 15 + 90 + 38 = 180 ， x = 37 度 48 ：角ABC = 180 - 105 = 75 度 so, x = 180 - 75 - 48 = 57 度 49 ：let 角BAD = x so , 角ADC = x + 25 因弧BD : 弧AC = 2:3 so , x / x+25 = 2/3 3x = 2x + 50 , x = 50 度