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Ninth grade, 53 math
Question 9: 2.25% (1-x) 2 =1.98%? X1= 6.19% x2 =1.93 (excluding)?

According to the S-section rectangle ABCD = s+s△BOC-s sector BOC, the length and width of the rectangle, the bottom and height of the equilateral △BOC, the radius and radian of the sector BOC are calculated respectively, and then solved according to the area formula: OE⊥BC with the intersection o as point E,

∵OB=OC,OE⊥BC,

∴∠BOE=? ∠BOC= 1/2? ×60 =30 ,

∴BE=? OB=? × 10 = 5mm;

In Rt△OEB, the root number of OE=5 is 3(mm).

OB = OC,∠BOC=60,

∴△BOC is an equilateral triangle, ∴BC=OB= 10(mm).

∴S section =S rectangular ABCD+S△BOC+S sector BOC=25× 10+? 1/2* 10×5 radical 3-1/6 * 3.14 *10 *10? ≈250+43.3-52.3=24 1(mm2)。