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### 数学九年级上第二章第五节《为什么是0.618 》课件ppt

§2.5为什么是0.618？

C

A

B

AC叫做AB和BC的比例中项

1

x

A

C

B

(不合题意,舍去)

(1) 小岛D和小岛F相距多少海里?

A

(2) 已知军舰的速度是补给船的2倍,军舰在由B到C的途中与补给船相遇于E处,那么相遇时补给船航行了多少海里?（结果精确到0.1海里）

D

B

E

C

F

~

45º

(1) 小岛D和小岛F相距多少海里?

A

D

200

?

B

E

C

F

200

x

∵两船速度之比为

?

(2) 已知军舰的速度是补给船的2倍,军舰在由B到C的途中与补给船相遇于E处,那么相遇时补给船航行了多少海里?(结果精确到0.1海里,其中 )

A

D

200

100

45º

∴相同时间内两船的行程之比为

B

E

F

C

200

2x

2x

∵ DE<AB

?

(2) 已知军舰的速度是补给船的2倍,军舰在由B到C的途中与补给船相遇于E处,那么相遇时补给船航行了多少海里?(结果精确到0.1海里,其中 )

A

D

200

x

100

45º

B

E

C

F

200

>200

(不合题意,舍去)

>0

(不合题意,舍去)

P—74页的 1，2

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