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1圆的周长演示器的自制分配的圆周长教具是以一个直径为1dm的圆为主体制成的。我用0．8cm厚的木板，制成了两个大小不同的圆，一个直径为5dm，另一个直径为5cm，并分别在两面涂上红漆，用黄色颜料标明圆心。在大圆的圆围上沿半径向国心锯一条约1cm深的窄缝，以便用钢卷尺量周长
A circular circumference demonstrator’s self-provisioned circular long teaching aid is made up of a circle with a diameter of 1 dm. I used 0.8cm thick wood to make two circles of different sizes, one with a diameter of 5dm and the other with a diameter of 5cm. I painted red paint on both sides and marked the center of the circle with yellow pigment. Slit a 1cm deep slit along the radius to the country’s center so that the perimeter can be measured with a steel tape measure.