An object is subjected to three * * * point forces on the same horizontal plane. If the resultant force of these three forces cannot be zero, what conditions should these three forces meet?

reverse thinking: when an object is balanced by three forces in the same plane, the vector line segments representing the three forces must form a closed vector triangle.

therefore, when the resultant force of these three forces is not zero, that is, the object cannot be balanced, so the vector line segments representing these three forces cannot form a closed vector triangle.

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