[求助]请教那道w.x.y.x.k为数轴五点的问题

chenxu

w.x.y.z.k从左至右依次排列在一数轴上, product of wxyzk < 0, 问哪一个必> 0?

Choices: wk,wx, zk, yz... Ans: zk ( 有点记不清了, 简单但有陷井,要小心)

horsefish:xy

我认为zk 和xy都行，这个画图就出来了。

不知道大家的看法如何？

calista5133

i agree:if w<0,then x,y,z,k >o,then xy>0,zk>0

if wxy<o,the result is the same

if wxyzk<0,the result is the same

tiger1234

zk: in order for w*x*y*z*k to be less than 0, an odd number of varibles among w, x, y, z, k must be less than 0, so if this number equals to 1, then k > z > y > x > 0, implies zk > 0; if the number is 3, then k > z > 0, implies zk > 0; if the number is 5, then z < k < 0, implies zk > 0; thus zk must be greater than 0 if w < x < y < z < k and w*x*y*z*k < 0;

xy: the same thing applies: if the number is 1, then k > z > y > x > 0, implies xy > 0; if the number is 3, then k > z > 0 and x < y < 0, implies xy > 0; if the number is 5, then x < y < z < k < 0, implies xy > 0;

so im guessing only one of these two is in the answer choices;

horsefish

同意ZK也是答案