Job Recruitment Website - Property management - 1. The radius of the inner circle of a ring is 4cm, and the width of the ring is 1cm. Find the area of the ring. 2. The central angle of the sector is 240 degrees, and the sector is in the circle.

1. The radius of the inner circle of a ring is 4cm, and the width of the ring is 1cm. Find the area of the ring. 2. The central angle of the sector is 240 degrees, and the sector is in the circle.

1, the radius of inner circle is 4cm, and the ring width is 1cm, so the radius of outer circle is 5cm, so S ring =S outer circle -S inner circle = 9 ∏ cm 2.

2. According to the formula of sector area, S sector = 240 * ∏ * 6 2/360 = 24 ∏ cm 2.