Question

What is the sum of the arithmetic sequence 3, 9, 15..., if there are 36 terms?

Answer 1

Sum of n terms = (n/2)[2a + d(n-1)]

where d = common difference and a = first term

Answer 2

common difference d = 9- 3 = 6

Answer 3

right then what do I do?

Answer 4

well plug in the values

n = 36, d = 6 and a = 3

Answer 5

plug these in and work it out

Answer 6

= (36/2)[2*3 - 6(36-1)]

Answer 7

sorry that should be a + before the 6 not -

Answer 8

you're all good so then I have to solve that?

Answer 9

do the parts in the parentheses first

Answer 10

(18)[35] is what I got but that doesn't seem like it makes sense at all

Answer 11

36/2 = 18
36 - 1 = 35

Answer 12

no thats not right its

18(6 + 6*35)

do the stuff in the parentheses first then finall y multiply by 18

Answer 13

7560?

Answer 14

multiply 6 by 35 before adding the 6

Answer 15

actually 3888

Answer 16

no i think you are doing things in the wrong order

remember
PEDMAS

Parentheses Exponent Division Multiplication Add Subtract

thats the order of operations

Answer 17

yes 3888 is correct

18(6 + 6*35
= 18*(6 + 210)
= 18 * 216
= 3888

Answer 18

thank you!

Answer 19

PEDMAS is very important

Answer 20

yw

Answer 21

note i worked out 6 + 210 before i multipilied by 18
because 6 + 210 was in the parentheses