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# 欢迎各位老师莅临指导 ! - PowerPoint PPT Presentation

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A

B

C

D

A

B

C

D

E

１. 画一个等腰梯形ABCD，过两底边AD、BC的中点 E、F画一条直线，将等腰梯形ABCD沿直线 EF对折。

E

F

50°

130°

130°

• （1）、若等腰梯形有一底角是50°，则

5cm

5cm

E

A

D

B

C

∵∠B=∠C（等腰梯形同一底上两个内角相等），

∴EB=EC（等角对等边），

∴EB-AB=EC-DC，

D

C

A

E

B

∴四边形AECD是平行四边形，CE=DA=CB=6

AE=DC=5（平行四边形的对边相等）

∴EB=AB－AE=8－5=3.

CE+EB+BC=6+3+6=15

• 在等腰梯形ABCD中，AB∥DC,CE ∥DA。AB=8，DC=5，DA=6，求△CEB的周长.

2、梯形ABCD中,AB//CD，DE//CB，ΔAED的周长为18，EB=4，求等腰梯形ABCD的周长。

１、定义：

2、等腰梯形的性质：