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# 义务教育课程标准实验教科书　浙江版 《 数学 》 八年级下册 - PowerPoint PPT Presentation

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6.1矩形(3)

BD = CD

A

C

B

D

A

C

B

D

E

AC + CE > AE

A

10

6

4

C

∴△ABD ≌△ECD

B

D

E

∵ AC² = 10² = 6² + 8² = AE² + CE²

∴△AEC是直角三角形

1

∴ SᇫABC = SᇫAEC =— × 6 × 8 = 24

2

E

B

∵ CD是斜边上的中线

∵ DE = CD

∴四边形ACBE是平行四边形

D

∴四边形ACBE是矩形

∴CE = AB

C

A

∴CD = ½AB

B

D

C

A

1、 如图：在RtΔABC中，CD是斜边AB上的中线，已知∠DCA=200，则∠ A＝＿＿，∠B＝____。

20°

70°

∵CD是斜边AB上的中线

(直角三角形的斜边中线等于斜边的一半）

∴∠Ａ＝∠ＤＣＡ＝２０°

∴∠Ｂ＝９０°－ ∠Ａ＝ ９０°－２０°＝７０°

（直角三角形两锐角互余）

2 、在Rt△ABC中，∠C=Rt∠，AC=BC=1，则AB边上的中线长为________

3 、如图，一斜坡AB的中点为D，BC=1，CD=2，则斜坡的坡比为______