數學Trigonometric Ratios

ABC is a sector. Its radius is 10cm and the angle at the centre is 70 degree. D is a point on AC such that BD is perpendicular to AC.
(a) Find the area of triangle ABD

A. cos 70deg = AD/10
AD = 10 cos 70deg cm

sin 70deg = BD/10
BD = 10 sin 70deg cm

area of triangle ABD
= (10 cos 70deg)(10 sin 70deg)/2
= 16.070cm^2(cor. to 3 d.p.)

(b) Find the area of the shaded region.

A. I guess the answer is (the area of sector) – (the area of the triangle)

area of the shaded region
= pi(10)^2(70deg/360deg)- (10 cos 70deg)(10 sin 70deg)/2
= 45.017cm^2(cor. to 3 d.p.)

(PS: deg stands for degree because Yahoo cannot show the degree symbol.)

If I have made a mistake, please tell me.

2010-05-22 00:28:12 補充：
BTW, please provide the diagram next time. Otherwise, no one will understand the question.

Can you provide the diagram??