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# 等腰三角形专题复习课 - PowerPoint PPT Presentation

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A. 3cm,4cm,5cm; B. 3cm,3cm,6cm

C. 4cm,7cm,4cm; D.1cm,2cm, cm

C

2.如果等腰三角形的顶角等于36°，则底角等于_________度；如果底角等于36°，那么顶角的度数为_________．

72°

108°

4.5

25

12cm2

5.等腰三角形有两边长分别为3cm和5cm，则此三角形的周

11cm或13cm

——分类思想

70°

70°

55°、 55 °

70°是顶角

70°是底角

55°、 70°或40°

D

C

C

D

B

A

B

A

50°、 130°

O

Ｃ1

C2

C4

C3

∠O为顶角

∠D为顶角

E

C

B

D

A

4、如图,在等腰△ABC中, ∠BAC=90°,AB=AC=1,

(不与B、C重合），在AC

A

120°

120°

C

B

40°

40°

20°

20°

A

A

120°

B

D

C

C

B

D

20°

40°

1.等腰三角形给你留下的印象是什么?

(1) 等腰三角形是轴对称图形,底边上的中线所在的直线是它的对称轴;

(2) 等腰三角形底边上的中线,高线和顶角的平分线是同一条线段(三线合一);

(3)有两个角(或两条边)相等的三角形是等腰三角形.

①角不确定，对角进行分类

②边不确定，对边进行分类

③三角形形状不明确，

2.解决有关等腰三角形的问题往往要用到的思想方法是什么?

2、学习了一种思想----分类思想