Arcs whose centers are vertexes A, C, E, G are drawn in right octagonal ABCDEFGH with one side 9 cm as shown in the figure below.
Find the area of the shaded portion.
Pi is assumed to be 3.14.
Answer
34.83 cm2
Solution
The inside of right octagon is separated and compared as shown in Fig.1 and 2.
The area of ☆ is equal.
According to Fig.2, the total area besides ☆ is 9 × 9 + 9 × 4.5 / 2 × 4 = 162 cm2.
Therefore the area to find is 162 - 9 × 9 × 3.14 × 45/360 × 4 = 34.83 cm2.
Find the area of the shaded portion.
Pi is assumed to be 3.14.
Answer
34.83 cm2
Solution
The inside of right octagon is separated and compared as shown in Fig.1 and 2.
The area of ☆ is equal.
According to Fig.2, the total area besides ☆ is 9 × 9 + 9 × 4.5 / 2 × 4 = 162 cm2.
Therefore the area to find is 162 - 9 × 9 × 3.14 × 45/360 × 4 = 34.83 cm2.
