Question

Find the sum of a finite arithmetic sequence from n = 1 to n = 15, using the expression 2n + 5.

315
215
32
35

Answer 1

@dan815

Answer 2

@welshfella

Answer 3

Please help! Ill give medals and become fan

Answer 4

what is the first term, when \(n=1\)?

Answer 5

I dont know

Answer 6

really?

Answer 7

replace \(n\) by \(1\) in \(2n+5\)

Answer 8

so its 7?

Answer 9

yes now hold that number

Answer 10

what is \(2n+5\) if \(n=15\)?

Answer 11

35?

Answer 12

yes

Answer 13

Is that the final answer?

Answer 14

formula you are going to use is
\[\frac{n}{2}(a_1+a_n)\] you have \(a_1=7,a_{15}=35\)

Answer 15

what is\(7+35\)?

Answer 16

Its 42

Answer 17

ok so we are at
\[\frac{15}{2}(42)\]

Answer 18

divide 42 by 2, then multiply the result by 15

Answer 19

Its 315