(2) Subtract two triangles from the parallelogram: (20×6- 16×6÷2×2=24 (square centimeter).
(3) directly calculate the extra small parallelogram on the right: (20- 16)×6=24 (square centimeter), as shown in the figure:
(4) Multiply the small triangle by 2: (20- 16) × 6 ÷ 2× 2 = 24 (square centimeter), as shown in the figure:
4. 1.4m = 14 decimeter, 0.9m =9 decimeter.
14÷2=7 (curved surface) 9÷2≈4 (curved surface) (note: rounding method)
7×4×2=56 (surface) (note: first make a square with a side length of 2 decimeters, so this square can be used as two small red flags).
This problem cannot be divided into large areas.
5. The shaded part is (r 2-r 2) ÷ 2 = 40, so r 2-r 2 = 80.
How much larger the area of a big circle is than that of a small circle is the area of a circular ring.
S=？ π (R2-R2) = 80 π = 80× 3.14 = 251.2 (square centimeter)