Given the first N-term of sequence an and Sn = 2n, find its general term formula

Given the first N-term of sequence an and Sn = 2n, find its general term formula

When n = 1, A1 = S1 = 2 * 1 ^ 2 = 2;
When n > 1:
Sn=2*n^2
S(n-1)=2*(n-1)^2=2(n^2-2n+1)=2*n^2-4n+2
So an = SN-S (n-1) = (2 * n ^ 2) - (2 * n ^ 2-4n + 2) = 4n-2
And A1 = 2 = 4 * 1-2, which conforms to the general formula, so the general formula of sequence {an} is 4n-2 = 2 (2n-1)

Find an = n + 1 / 2n (general term formula), find n term and Sn

You have copied the wrong question
Find an = n + 1 / 2 ^ n (general term formula), find n terms and Sn
Otherwise, the original problem in high school stage no solution. If so, continue to ask

First n terms and Sn = 2n + 1 to find the general term formula an!

sn=2n+1
When n = 1, A1 = 3
n> At 1:00,
an=Sn-S(n-1)
=2n+1-[2(n-1)+1]
=2n+1-2n+1
=2

If the vectors a and B are all non-zero vectors and the direction a * B ≤ 0, then the value range of the angle between a and B is determined

Let the angle between vector a and vector b be X,
Vector a * vector b = |a | * |b | * cosx ≤ 0,
Because | a | and | B | are all greater than zero, then there is
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