5條數學mc 10點:)

18)

空氣體積 : 錐體體積 = (14 : 30)^3 = 343 : 3375
水體積 : 錐體體積 = 3032 : 3375
(h : 30)^3 = 3032 : 3375 => h = 28.9


20)

第一組 :
mode = a + 1,
median = a + 1,
inter-quartile range = (a + 4) - (a - 1) = 5

第二組 :
mode = all or nothing,
median = (a + a + 2)/2 = a + 1,
inter-quartile range = (a + 3) - (a - 2) = 5


22)

3i^2 + (a + 1)i + 1/i = -b + 2i
3(-1) + (a + 1)i + i/i^2 = -b + 2i
-3 + (a + 1)i + i/(-1) = -b + 2i
-3 + (a + 1)i - i = -b + 2i
-3 + ai = -b + 2i


23)

2^(2x) - 9[2^(x + 2)] + 128 = 0
2^(2x) - 9[2^(x)][2^(2)] + 128 = 0
2^(2x) - 36[2^(x)] + 128 = 0
[2^(x)]^2 - 36[2^(x)] + 128 = 0
2^(x) = 4 or 2^(x) = 32
x = 2 or x = 5

log a + log b = log 2 + log 5 = log 10 = 1


28)

join OB, you will see an isosceles triangle with base angles = 10
i think the answer should be C

To xx ( 小學級 5 級)：

第22題會唔會有d....