F5 Maths

2010-09-27 1:59 am

figure: http://img823.imageshack.us/img823/3237/69194653.jpg

In the figure, A, B, C and D are points lying on the circle. If AB = 5, AD = 3 and BD = 7, then angle BCD =

A. 60
B. 85
C. 95
D. 120

回答 (2)

2010-09-27 2:24 am

✔ 最佳答案

Cos A = (5^2 + 3^2 - 7^2) / [(2)(5)(3)]

Cos A = - 1/2

A = 120°

A + C = 180° (圓內接4邊形對角互補)

120° + C = 180°

C = 60°

Answer : (A)

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2010-09-27 2:14 am

但我計到96既?!

咁C囉

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