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# 四边形中的动态问题 - PowerPoint PPT Presentation

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## PowerPoint Slideshow about '四边形中的动态问题' - jemima

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1、掌握动态问题的基本解题方法，

2、培养合作意识，学会合作学习。

C

B

A

P

1cm/s

1、 如图： ABCD中，AB=7，BC=4，∠A=30°

△PBC为等腰三角形？

3、Rt△PMN中，∠P＝90°，PM＝PN，MN＝8cm，矩形ABCD的长和宽分别为8cm和2cm，C点和 M点重合，BC和MN在一条直线上。如果Rt△PMN不动，矩形ABCD沿MN所在直线向右以每秒1cm的速度移动，直到C点与N点重合为止。设移动x秒后，矩形ABCD与△PMN重叠部分的面积为y，求y与x之间的函数关系式？

P

A

D

2

N

B

8

M

8

C

D

∴y= x2 (0≤x≤2)

2

B

8

C

P

A

D

G

E

2

B

8

M

F

8

N

C

∵MC＝x，∠PMN＝450

∴CE＝x，

A

D

D

∴y重叠＝S梯形MCDG＝ （x-2+x）2=2x-2

2

8

B

B

C

C

P

H

G

F

M

8

T

N

∵MC＝x，ＭＦ＝ＧＦ＝２,

∴CF＝GD= x-2

∴y = 2x-2 （ ２＜x≤６ ）

A

D

D

＝12－ (8－x)2

B

C

C

B

P

H

G

Q

F

T

M

8

N

∴y＝S五边形GMCQH＝Ｓ梯形ＧＭＮＨ－ＳΔＱＣＮ