?? one jj

workhard77

93、DS题(记不太清此题，大意如后): y=x^2+C, 问y总在X轴之上吗？
（1）C>0
（2）y过某点（a,b）(a,b确定)
【确定】 A
R：  y=x^2+C值始终为正


----------why not "D"?

gansen

画出xy坐标，当c>0时，该图形就一个与y轴半版轴相交的U(忘了叫什么了），所以总在x轴之上。答案是A

[此贴子已经被作者于2002-9-20 16:20:49编辑过]

workhard77

but, why 2) is not right?
through it we can also get C

tongxun

C is a wrong answer, because we can get a clear answer by the condition 1).
But if (a,b) means a certain point, you can use these numbers to check whether the curve is above the y zhou.

workhard77

Sorry, I think you've misunderstand me. What i mean by "c" is not the answer "C" but the parameter C in the equality "y=x^2+c".
Maybe I did not express myself clearly.

Then, can you explain me why the answer "D" is not right?

workhard77

But if (a,b) means a certain point, you can use these numbers to check whether the curve is above the y zhou.
----------------------------------------------
Why "y zhou"? I think we can get the number C by "c=y-x^2=b-a^2", that will be a certain number because (a, b) is certain. Then we can know whether y>0.
So condition 1) and 2) are all right by itself.
Why not "D"?

tongxun

我误会了你的意思。你也误会了我的意思。我说“use these numbers to check whether the curve is above the y zhou.”就是指Y=C，可以通过此点求出。从而确定是否总在上访啊！
D

lcbfeng

就是说即便是(a,b)确定，c也还是有可能小于0，那种状况不能保证Y>O,不唯一

workhard77

tongxun, lcbfeng: 请问两位版主答案到底是什么呀？我有点弄糊涂了，不好意思。：）