The area U2 of the colored part reported inNo. 18, Volume 1, Mathematics People's Education Edition, Grade 6.
Do it according to the principles of inclusion and exclusion.
Shadow area = large sector area+small sector area-rectangular area
=3. 14×3? ÷4+3. 14×2? ÷4-2×3
=7.065+3. 14-6
=4.205