Some urgent questions

1. If x+1, 3x-2 and 2x+4 are three consecutive terms of an arithmetic sequence, then the sum of the first and the third number will be 2 times of the second number.
This means :
(x+1) + (2x+4) = 2(3x-2)
3x+5 = 6x-4
9 = 3x
x = 3
2. Total 15 numbers :
12,18,24,30,36,42,48,54,60,66,72,78,84,90,96

應該是

[(x 1) (2x 4)]/2 = 3x - 2

因為他們是連續數的關係
最細和最大加起來除2就會等於中間那個了
你可以隨意想三個連續數來證明的


另一個方法是
Let y be the difference between the numbers
x + 1+y=3x-2 <--最細那個加上y的差別等於中間那個
3x-2 +y = 2x +4 <--中間那個加上y的差別等於最大那個

然後再求x了
答案都應該相同的

1. [(x + 1)+(2x + 4)]/c = 3x - 2
x=3 (4, 7, 10)

2. 15 (12, 18, 24, 30, 36, 42, 48, 54, 60, 66, 72, 78, 84. 90. 96)