AB is the diameter of the given circle, while points C and D lie on the circumference as shown. If AB is 15cm, AC is 12 cm and BD is 9 cm, find the area of quadrilaterial ACBD.

Angle ACB = 90 degrees

(since diameter of a circle subtends 90 degrees at all points on its circumference)

Now AB = 15

 and AC = 12

By Pythagorous theorem

we find BC = 9

Area of triangle ABC = Area of triangle BAD

(all the 3 sides of the triangles are equal)

Area of ACBD = 2 X 1/2 X AC X CB

= 108 cm²