For the size of the sector, first measure the distance from the outer circle to the center of the sector as the radius r, then measure the distance from the inner circle to the center of the sector r, and measure the angle of the center of the circle after the whole sector is opened. With these data, you can calculate the data such as the area you want.

As the name implies, a sector is a sector face, which is geometrically defined as a sector. The figure surrounded by an arc and two radii passing through the two ends of the arc is called a sector, so is the sector a surface? Actually, it is not. Now it refers to a form of calligraphy and painting, which is divided into folding fan and round fan.

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When you mention a fan, you will inevitably think of a fan, a talented person and a beautiful woman, and a fan in hand. In the history of China, painters and calligraphers of all ages like to paint or write on fans to express their feelings, or collect poems for others or give them to friends as souvenirs. The fan for storing calligraphy and painting is called a fan, which is framed into a book for easy collection.

So the so-called plate is actually a conventional name. China's fan culture has profound cultural connotations and is an integral part of national culture. China has always been called the kingdom of making fans.