标题: math jj , pls [打印本页] 作者: joywzy 时间: 2003-3-11 23:09 标题: math jj , pls
1）DS. Is x<0?
a) x^3 + x < 0 ==> x(x^2 +1) < 0 == > x , 0. Everyone agree A is right
b) x^3 + x + 1 = 0 ==> x(x^2 + 1) = -1 == > x < 0
but someone said there is no real number resolution for B. so answer is A.
D or A? do DS question really cares about exact answers?
【讨论】我认为是A，因为B方程无解。请其他机委提供看法作者: oddyuibe 时间: 2003-3-12 00:14
I think the answer is D
1) x^3+x<0;;;x*(x^2+1)<0 since x^2+1>0, so x<0
2) x^3+x+1=0;;;x*(x^2+1)=-1 since x^2+1>0,so x<0
Thus, in my point of view, the answer should be D作者: oddyuibe 时间: 2003-3-12 00:18
Personally,I think in DS,what we have to approve is whether x is in this range,while not a specific answer. Anyway, I think there should be a definite answer to condition 2, just beyond our capacity to work it out.作者: qiqi 时间: 2003-3-12 14:29
