To prove that quadrilateral STUV is a parallelogram, one of the following conditions must be satisfied:
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Both pairs of opposite sides are parallel: If \( ST \parallel UV \) and \( SU \parallel TV \), then STUV is a parallelogram.
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Both pairs of opposite sides are equal in length: If \( ST = UV \) and \( SU = TV \), then STUV is a parallelogram.
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One pair of opposite sides is both parallel and equal: If \( ST \parallel UV \) and \( ST = UV \), or \( SU \parallel TV \) and \( SU = TV \), then STUV is a parallelogram.
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Diagonals bisect each other: If the diagonals (SU and TV) bisect each other at point O, then STUV is a parallelogram.
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Using angle properties: If one pair of opposite angles are equal, then the quadrilateral is a parallelogram. For example, if \( \angle S = \angle U \) and \( \angle T = \angle V \), then STUV is a parallelogram.
Any one of these conditions is sufficient to prove that STUV is a parallelogram.