你地會點prove which of the following is/are true? (a) If a < b and x < y, then (i) a + x < b +y (ii) a - x < b - y (iii) ax < by (iv) a/x < b/y?

2015-12-21 1:32 pm

更新1:

你地會點prove? which of the following is/are true? (a)If a < b and x < y, then (i)a + x < b +y (ii)a - x < b - y (iii)ax < by (iv) a/x < b/y? 編輯

更新2:

你地會點prove? which of the following is/are true? (a)If a < b and x < y, then (i)a + x < b + y (ii)a - x < b - y (iii)ax < by (iv) a/x < b/y?

回答 (1)

螞蟻雄兵

2015-12-21 1:59 pm

Sol
(i) a + x < b + y is true
(ii)
Set a=3，b=4，x=5，y=6
a－x=3－5=－2
b－y=4－6=－2
a－x=b－y
錯
(iii)
Set a=3，b=4，x=－1，y=－2
ax=－3，by=－8
ax>by
錯
(iv)
Set a=－3，b=－4，x=－1．y=－2
a/x=3，b/y=2
ax>by
錯

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