Fold a circular piece of paper with a diameter of 8 cm in half to get a semicircle. The area of the circle is

Fold a circular piece of paper with a diameter of 8 cm in half to get a semicircle. The area of the circle is

8÷2=4cm
3.14×4²=50.24（cm²）…… Area of a circle

(1) A ring armour (Fig. 1) has an outer diameter of 8 cm and a ring width of 1 cm
① If such two rings are buckled together and tightened (as shown in Figure 2), the length is______ (2) if n such rings are connected and tightened, the length is______ (2) another kind of ring B, like ring a in (1), is buckled and tightened. ① the length of three ring B is 28cm, and the length of five ring B is 44cm, and the outer circle diameter and width of ring B are calculated. ② the existing n (n ＞ 2) ring a and n (n ＞ 2) ring B are buckled and tightened as in (1). How many cm is the length?

(1) (1) according to the figure, if the two rings are buckled together and tightened, the length is 2 inner circle diameters + 2 ring widths, and the length is 6 × 2 + 2 = 14cm; ② According to the above rules, if n such rings are connected and tightened, the length is 6N + 2; therefore, the answer is 14, 6N + 2; (2) if the outer diameter of ring B is xcm and the ring width is YCM, then according to the meaning of the question: 3x − 4Y = 285x − 8y = 44, then x = 12Y = 2, answer: the outer diameter of ring B is 12cm and the ring width is 2cm. ② the diameter of ring B is 12 and the ring width is 2 Suppose that a total of 2n rings are connected, and the two ends are also connected, that is, 2n small rings are connected to form a big ring, then the total length is (12 + 8) n - (2 + 4) n = 14N, then there are three cases: A. both ends are a, that is, to untie a place where two a are connected, so the total length is 14N + 2B. Both ends are B, that is, to untie a place where two B are connected, so the total length is 14N + 4C The head is one a and one B, that is to untie a place where a and B are connected, so the total length is 14N + 3

For a ring, the diameter of the outer circle is 3 / 2 times of the diameter of the inner circle, and the area of the ring is 150 square centimeters. Calculate the area of the outer circle

The area of the outer circle is s, the area of the inner circle is 4S / 9, and the area of the ring is 5S / 9 = 150, s = 270 square centimeters