1. 定义：我们把空间中具有大小和方向的量叫做空间向量．向量的大小叫做向量的长度或模.

→ 举例？ 表示？(用有向线段表示) 记法？　 → 零向量？　 单位向量？ 相反向量？

→ 讨论：相等向量？　 同向且等长的有向线段表示同一向量或相等的向量．

→ 讨论：空间任意两个向量是否共面？

4. 三个力都是200N，相互间夹角为60°，能否提起一块重500N的钢板？

3. 向量的运算运算律：加法交换律：+＝+

2. 向量的加减以及数乘向量运算：

向量的加法：

向量的减法：

实数与向量的积：

实数λ与向量的积是一个向量，记作λ，其长度和方向规定如下：|λ|＝|λ|||　(2)当λ＞0时，λ与同向； 当λ＜0时，λ与反向； 当λ＝0时，λ＝.

1、有关平面向量的一些知识：什么叫做向量？向量是怎样表示的呢？

既有大小又有方向的量叫向量．向量的表示方法有：用有向线段表示；用字母、等表示；

用有向线段的起点与终点字母：．长度相等且方向相同的向量叫相等向量.

65.(　　 )Margarite Santos was a student of biology first and then she turned to　　　 .

A. language　　 B. math　　 C. gerontology　　 D. art

64.(　　 )What is the approximate number of the old people in 1995?

A.5.3million　　 B.41.4million　　 C.3.0million　　 D.74million

63.(　　 )The aging of America means　　　　　 .

A. more crimes in society　　　　　　 B. more unemployment

C. more job opportunities　　　　　　 D. more requirements

62.(　　 )What does the underlined sentence in Para.1 mean?

A. America has suddenly become a nation of old people.

B. Gerontology has suddenly become popular .

C. More elderly has professors are found in American colleges

.D. Older students begin to be admitted into American colleges.

61.(　 )Many investors think lotteries

A. can provide them with more fortune

B. provide them with a chance to have a piece of the action

C. are stock markets for poor people

D. are no better than legalized gambling

E

For an increasing number of students at American universities,　 old is suddenly in. The reason is clear: the aging of America means jobs. Besides the aging of body-boom population, a longer life means that the nation’s elderly population is certain to grow greatly over the next 50 years. By 2050, 25 percent of all Americans will be older than 65,up from 14 percent in 1995.The change causes some problems for government and society, of source .But it also creates jobs in medicine and health fields and in law and business as well.“Besides the doctor, we’re going to need more sociologists, biologists, city planners and lawyers,” says Professor Edward Schneider of the University of Southern California’s (USC) School of Gerontology.

Lawyers can major in “elder law”, which covers everything including nursing-home abuse and age discrimination. Businessmen see huge opportunities in the elder market because the baby boomers,74 million strong , are likely to be the wealthiest group of retire in human history.“Any student who combines an expert knowledge in gerontology (老人学) with , say , an MBA or law degree will have a license to print money,” one professor says.

Margarite Santos is a 21-year-old senior at USC She began college as a biology major but found she was “really bored with biology”.So she took a class in gerontology and discovered that she liked it .She says,“really bored with biology ”.So she took a class in gerontology and discovered that she liked it .She says,“I did volunteer work in retirement homes and was very satisfied.”

根据短文内容，选择最佳答案。