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# 第 27 课时　梯形 - PowerPoint PPT Presentation

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## PowerPoint Slideshow about '第 27 课时　梯形' - moira

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1．梯形的定义及分类；

2．梯形的中位线及有关计算．

(1)求证：△ABE≌△CDA;

(2)若∠DAC＝40°，求∠EAC的度数．

1．等腰梯形两腰的大小关系，两底的位置关系；

2．等腰梯形在同一底上的两个角的大小关系；

3．等腰梯形的对角线的大小关系．

1．定义法；

2．从同一底上的两个角的大小关系来判定梯形是等腰梯形；

3．从两条对角线的大小关系来判定梯形是等腰梯形．

∴∠B＝∠DEC.

∵∠DEC＝∠C，∴∠B＝∠C.

∴梯形ABCD是等腰梯形．

1．常用辅助线；

2．动态几何问题；

3．梯形与全等、相似、解直角三角形等知识的综合运用．

∴∠B＝60°

A．b2＝ac B．b2＝ce

C．be＝ac D．bd＝ae

A