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问题 解答题

在△ABC中，a，b，c分别为内角A，B，C的对边，且2asinA=(2b+c)sinB+(2c+b)sinC，

(Ⅰ)求A的大小；

(Ⅱ)求sinB+sinC=1，试判断△ABC的形状。

答案

解：（Ⅰ）由已知，根据正弦定理，得2a2=(2b+c)b+(2c+b)c，

即a2=b2+c2+bc，

由余弦定理，得a2=b2+c2-2bccosA，

故。

(Ⅱ)由(Ⅰ) ，得sin2A=sin2B+sin2C+sinBsinC，

又sinB+sinC=1，得sinB=sinC=，

因为0°＜B＜90°，0°＜C＜90°，

故B=C，

所以△ABC是等腰的钝角三角形。

单项选择题 案例分析题

Shopping habits in the United States have changed greatly in the last quarter of the 20th century. （1） in the 1900s most American towns and cities had a Main Street. Main Street was always in the heart of a town. This street was （2） on both sides with many （3） businesses. Here, shoppers walked into stores to look at all sorts of merchandise: clothing, furniture, hardware, groceries. （4）,some shops offered （5） .These shops included drugstores, restaurants, shoe-repair stores, and barber or hairdressing shops. （6） in the 1950s, a change began to （7） .Too many automobiles had crowded into Main Street （8） too few parking places were （9） shoppers. Because the streets were crowded, merchants began to look with interest at the open spaces （10） the city limits. Open space is what their car-driving customers needed. And open space is what they got （11） the first shopping centre was built. Shopping centres, or rather malls, （12） as a collection of small new stores （13） crowded city centres. 14 by hundreds of free parking space, customers were drawn away from （14） areas to outlying malls. And the growing （16） of shopping centres led （17） to the building of bigger and betterstocked stores. （18） the late 1970s,many shopping malls had almost developed into small cities themselves. In addition to providing the （19） of one stop shopping, malls were transformed into landscaped parks, （20）benches, fountains, and outdoor entertainment.

请在4处填上正确答案（）

A.Apart from

B.However

C.In addition

D.As well
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单项选择题

合同订立过程中，承诺自（）时生效。

A.发出

B.要约人了解其内容

C.合同生效

D.到达要约人
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