Question

Please and thank youuuuu!
What is the 23rd term of the arithmetic sequence where a1 = 7 and a5 = 21?

Answer 1

first find the common difference
can u do that?

Answer 2

Im not really sure what you mean?

Answer 3

you have to find how far the first number is from the second one. that's the common difference.

Answer 4

arithmetc series can be written as

a, a+d, a+ 2d, a + 3d, ....
common difference d is added to each term to get the next term

Answer 5

a1 is first term and a5 is the fifth so 4 'd's have been added to get from a1 to a5

do you follow that ?

Answer 6

got it

Answer 7

ok so if we work out a5 - a1 and divide by 4 we get d
so
21-7 / 4 = 14/4 = 3.5

d = 3.5

Answer 8

general form for nth term = a1 + (n-1)d
so 23rd term = 7 + (23-1)3.5
= 7 + 22*3.5

Answer 9

84, thanks!

Answer 10

thats right - yw