问题 选择题

关于x的方程kx2+2x-1=0有两个实数根,则k的取值范围是(   )

A.k≥1

B.k≥-1

C.k≥1且k≠0

D.k≥-1且k≠0

答案

答案:D

本题考查的是根的判别式。方程有两个实数根,则根的判别式△≥0,建立关于k的不等式,求得k的取值范围,且二次项系数不为零。解题过程如下:∵a=k,b=2,c=-1,∴△=b2-4ac=4+4k≥0,即k≥-1时方程有两个实数根,又∵二次项系数不为零k≠0

∴k≥-1且k≠0,故选D

单项选择题
单项选择题

(五)

A characteristic of American culture that has become almost a tradition is to respect the self- made man—the man who has risen to the top through his own efforts, usually beginning by working with his hands. While the leader in business or industry or the college professor occupies a higher social position and commands greater respect in the community than the common laborer or even the skilled factory worker, he may take pains to point out that his father started life in America as a farmer or laborer of some sort.

This attitude toward manual labor is now still seen in many aspects of American life. One is invited to dinner at a home that is not only comfortably but even luxuriously furnished and in which there is every evidence of the fact that the family has been able to afford foreign travel, expensive hobbies, and college education for the children; yet the hostess probably will cook the dinner herself, will serve it herself and will wash dishes afterward, furthermore the dinner will not consist merely of something quickly and easily assembled from contents of various cans and a cake or a pie bought at the nearby bakery. On the contrary, the hostess usually takes pride in careful preparation of special dishes. A professional man may talk about washing the car, digging in his flowerbeds, painting the house. His wife may even help with these things, just as he often helps her with the dishwashing. The son who is away at college may wait on table and wash dishes for his living, or during the summer he may work with a construction gang on a highway in order to pay for his education.

The expression " wait on table" in the second paragraph means "()".

A.work in a furniture shop

B.keep accounts for a bar

C.wait to lay the table

D.serve customers in a restaurant