in the diagram AB=20 cm, BC=21 cm, AD=10 cm and DE= 10.5 cm. Angles ABC and ADE are right angles. if triangleADE is removed from triangleABC.What is the area of shaded region that remains?

Answer 1

Missing information: presumably A, D, B are colinear.

For right angle XYZ, |∆XYZ|=(1/2)(XY×YX)

So:
|∆ABC|-|∆ADE| = (1/2)(AB×BC)-(1/2)(AD×DE)