190. 18785-!-item-!-187;#058&011838
r s t
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On the number line shown, is zero halfway between r and s?
(1) s is to the right of zero.
(2) The distance between t and r is the same as the distance between t and -s.
Ans. C
還是想不透 (2)
因為 on the number line shown, t>s>r
所以若l t - r l = l t - (-s) l
when t<0 --> s<0, r<0, and s=r ==>impossible: t>s>r
when t=0 --> s<0, r<0, and s=r ==>impossible: t>s>r
when t>0 --> if s>0 and r>0 --> s=r ==>impossible: t>s>r
if s<0 and r<0 --> s=r ==> impossible: t>s>r
if s>0 and r<0 --> s=-r ==>zero is halfway between r and s
when s=0 --> t-r ≠ t-s
還是想不透為什麼答案是 C
因為在t>s>r的條件下,要滿足(2),0 就會分別在 r 與 s 之間了,不是嗎?