I'm not sure what I'm doing wrong. Will give brainliest, thanks in advance! (Arithmetic sequences)

A_165 = 5+(165-1)2

A_165 = 5+(164)2

A_165 = 5+328

A_165 = 333

Step-by-step explanation:

Hope this helps, also tell me if I'm worng or right!

Sn = n^2+4n, and n = 11

Step-by-step explanation:

Sorry that i'm late, but i think i see what you did wrong here;

What you entered in as that Sₙ = 2n + 3, but instead the nth term (aₙ) was equal to 2n + 3. How? Well you know the following formula;

aₙ = a₁ + (n-1)d

here the difference = 2 & a₁ = 5

aₙ = 5 + 2(n-1) = 5 + 2n - 2 = 2n + 3

So the aₙ = 2n + 3, not Sₙ. The sum of the series would be calculated using the following formula:

Sₙ = n/2[2a₁ + d(n-1)]

= n/2[2(5) + 2(n-1)] = n^2+4n

Now then we have to determine n where the series sum is 165. Let's plug in this value;

165 = n^2 +4n,

n = 11 & n = -15

n has to equal 11 here

(I hope this helps future students)

1,918

step-by-step explanation: