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How to do the third and fourth questions of the third chapter P 149 of ninth grade mathematics published by Beijing Normal University?
3. Solution: Let the radius of this tire be r meters, and we can get the following from the problem:

r？ =﹙0.72÷2﹚? ﹢﹙R-0.25﹚？

r？ =0. 1296+R？ -0.5R+0.0625

R ≈ 0.384 (m)

Let the radius of this tire be r meters.

4. Solution: CD=CE

Proof: connecting OC,

∫ Arc AC= Arc BC

∴∠DOC=∠EOC

And e are the midpoint of radii OA and OB, respectively.

∴OE=OD

OC = OC reappears.

∴△OCD≌△OCE(SSS)

∴CD=CE (the corresponding sides of congruent triangles are equal)

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