Rectangular area+1/4 circular area-large right triangle area = shadow area

2a×a+ 1/4×3. 14×a×a- 1/2×(2a+a)×a

=2a？ +0.758a？ - 1.5a？

= 1.285a？

When a=2cm. Shadow area: 1.285a? = 1.285×2? =5. 14(cm？ )