If A1, A2,..., a8 are arithmetic sequences with all items greater than zero and the tolerance D is not equal to 0, then () a a1a8 > a4a5 B a1a8a4 + A5 D a1a8 = a4a5 If the general term of {an} is an = 2n + 1, then the sum of the first n terms of {BN} determined by BN = (a1 + A2 +. + an) / N (n belongs to positive integer) is () a n (n + 1) B N (n + 1) / 2 c n (n + 5) / 2 D n (n + 7) / 2

If A1, A2,..., a8 are arithmetic sequences with all items greater than zero and the tolerance D is not equal to 0, then () a a1a8 > a4a5 B a1a8a4 + A5 D a1a8 = a4a5 If the general term of {an} is an = 2n + 1, then the sum of the first n terms of {BN} determined by BN = (a1 + A2 +. + an) / N (n belongs to positive integer) is () a n (n + 1) B N (n + 1) / 2 c n (n + 5) / 2 D n (n + 7) / 2

The first one is 1 2 3 4 5 6 7 8 B. don't be stingy. Just give me an example
The second assumption is A1 = 3, then A2 = 5, then B1 = 3, B2 = 4, which leads to the calculated result C
In fact, the most important thing to make a choice is to use your brain. Don't hum with a pen

If a1 + A2 = 3, A2 + a3 = 6, then A7 =?

Because GP, a1 + A2 = 3, A2 + a3 = 6
a1+a1*q=3,a2+a2*q=6
The division of the two formulas leads to A2 / A1 = 2
That is, the common ratio is 2
Substituting A1 = 1
So the general formula is: an = 2 ^ (n-1)
So A7 = 2 ^ (7-1) = 2 ^ 6 = 64

The general term an = (2 / 3) ^ n-1 [(2 / 3) ^ n-1 - 1] of known sequence {an} is expressed correctly
1. The maximum term is 0 and the minimum term is - 20 / 81
2. The maximum item is 0 and the minimum item does not exist
3. The maximum term does not exist and the minimum term is - 20 / 81
4. The maximum term is 0 and the minimum term is A4
But how can I calculate that the minimum term does not exist
How to make it - 20 / 81

Let t (t-1) = (t-1 / 2) ^ 2-1 / 4
2 / 3 ^ (n-1) = 1 / 2
N = log (2 / 3) (1 / 2) + 1 > 2 and

In the following formulas, the general term formula that cannot be used as sequence {an} is
1. An = root (n-2) 2. An = log (n-1) ^ (n-2) 3. An = 1 / (n ^ 2 + N + 1)
4.an = tan (n ∏)/4
A 1 B 2 C 1,2 D,1 ,2 4
Why D

1, n = 1
2, n = 1,2
4,n=2,6,10,…… It doesn't make sense
So choose D