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| 51. | circle centered at the origin of a Cartesian coordinate system, the arc being of length x and measured counterclockwise |
| 余弦以笛卡儿坐标系原点为圆心的单位圆的圆弦端点的横坐标，弧的长度为x，如果x为正，弧的长度则从（１，0）点按逆时针方向算起，若x为负，则按顺时针方向从（１，0）点算起 |
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| 52. | with thread about 80%.Turn the adjustment screw 2 clockwise to increase the bobbin thread amount or counterclockwise |
| 用绕线量调节螺丝2进行调节，让线绕到80% 。向右转动绕线量调节螺丝2绕线量变多，向左转动则变小。 |
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