1. if a:b=2:3 , a:c=3:4 and a:d=4:5, then b:c:d=?
A. 2:3:4
B. 3:4:5
C. 3:6:10
D. 18:16:15
E. 40:45:48
2. The largest value of (3cos2x-1)^2 +1 is
A. 2
B. 5
C. 17
D. 26
E. 50
2題CE OF MATHS
2011-07-25 2:20 am
回答 (1)
2011-07-25 2:30 am
✔ 最佳答案
1)
a : b = 2 : 3
2b = 3a
b = (3/2)a
;
a : c = 3 : 4
4a = 3c
c = (4/3)a
;
a : d = 4 : 5
4d = 5a
d = (5/4)a
So
b : c : d
= 3/2 : 4/3 : 5/4
= 12(3/2) : 12(4/3) : 12(5/4)
= 18 : 16 : 15
Answer : (D)
2)
Since - 1 ≤ cos2x ≤ 1 ,
(3cos 2x - 1)² + 1
≤ (3 (- 1) - 1)² + 1
= 17
Answer : (C)
收錄日期: 2021-04-21 22:21:41
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