Question

MEDAL!!!

Find the sum of the arithmetic series described.

d = 2, n = 26, \(a_n\) = 42

Answer 1

@welshfella @zepdrix

Answer 2

hmmm
i think you need to find the first term
a1 = 42 - 25(2) = -10

so S26 = (26/2) [-10 + 42]

Answer 3

Why did you make that equation for finding the first term?

Answer 4

well i intended to use
Sn = (n/2) [ a1 + l] where l = last term

Answer 5

not sure if that was is right .....

Answer 6

can i use the explicit formula for finding the first term?

Answer 7

No - its -8 I cant count!!

Answer 8

2(25) + a1 = 42
a1= -8

Answer 9

yes

Answer 10

now you can use (26/2) [ -8 + 42]

Answer 11

i got 442

Answer 12

yea

Answer 13

thank you! can you help me with two more questions?

Answer 14

i cant I have to go right now

Answer 15

ok thanks for your help though!