F. 6 數學題

The answer is : D. I and II only

I. True
If a > b > c
then ∠A > ∠B = ∠C (larger ∠ tolonger side)

II. True
b + c > a
(In a Δ, the sum of any two sides must be greater than the third side.)

III. False
This is false if ∠A is an obtuse angle.

2014-09-13 21:01:51 補充：
III.
The sum of interior angles of a Δ = 180°
If ∠A is an obtuse angle (> 90°),
then ∠B + ∠C < 90°
Hence, ∠B + ∠C < ∠A

這條MC的答案是D

I 大邊對大角﹐所以angle A > angle B > angle C

II 三角形兩邊之和大於第三邊﹐所以b + c > a

這樣已經可以判斷答案是D

III 未聽聞過三角形兩角之和大於第三角。但我們可以幻想a 很長﹐這樣角A就會很大而角B和C則很小﹐因此angle B + angle C > angle A 是不一定成立