下述几个判定平行四边形的假命题,由于其迷惑性较大,实在是有澄清之必要.假命题1一组对边平行,另一组对边相等的四边形是平行四边形.反例:等腰梯形一组对边平行,另一组对边相等,但它不是平行四边形.假命题2一组对边相等且一组对角相等的四边形是平行四边形.反例:如图1,作正三角 The following several false propositions for the determination of parallelograms, because of its greater deceptiveness, are in fact necessary for clarification. False Proposition 1 A group of opposite sides is parallel, and the other group of equal sides is a parallelogram. Counterexample: Isosceles Trapezoidal sets of parallel sides are parallel and the other set of opposite sides are equal, but it is not a parallelogram. False Proposition 2 A group of opposite sides is equal and a group of diagonally opposite quadrilaterals is a parallelogram. Counterexample: As shown in Figure 1, making a positive triangle