F2 數學 急

http://img171.imageshack.us/img171/2236/dogxgf.jpg

(a) Let BP= k metre
Radius of the blue part = 5m
Area of the blue part is (丌5^2)/2 =12.5丌

Radius of the red part = 5 - BP = 5-k
Angle XBY = 180 - 60 = 120
Area of the red part = 丌(5-k)^2(120/360)

Total area = 12.5丌 + 丌(5-k)^2(120/360) which is 43
丌(5-k)^2(120/360) = 43 - 12.5丌
丌(5-k)^2(120/360) = 3.73
(5-k)^2 = 3.56
5-k = 1.89
k= 3.11m

BP = 3.11 m

(b) the distance the dog travelled = arc AX + arc XY

=2丌(5)/2 + 2丌(1.89)*(120/360)

=19.66m