Question

.What is the 24th term of the arithmetic sequence where a1 = 8 and a9 = 56?

134

140

146

152

Answer 1

\(\large\color{midnightblue}{ \rm a_9=a_1+d(9-1) }\)

\(\large\color{midnightblue}{ \rm a_9=a_1+8d }\)

you know the \(\large\color{midnightblue}{ \rm a_1 }\) and the \(\large\color{midnightblue}{ \rm a_9 }\), solve for the difference

Answer 2

After you solve for the difference, use

\(\large\color{midnightblue}{ \rm a_{n}=a_1+d(n-1) }\) , or in your case, use

\(\large\color{midnightblue}{ \rm a_{25}=a_1+24d }\)

Answer 3

Tell me if you need more help

Answer 4

Wait, Where did A25 Come from? o-o

Answer 5

My bad

Answer 6

Well, \(\large\color{midnightblue}{ \rm a_{n}=a_1+d(n-1) }\) in your case would be

\(\large\color{red}{ \rm a_{24}=a_1+23d }\)

Answer 7

Have you found the difference yet ?

Answer 8

I Got 6.

Answer 9

yes good !

Answer 10

\(\large\color{midnightblue}{ \rm a_{24}=8+23(6) =? }\)

Answer 11

see what I am doing ?

Answer 12

146?

Answer 13

Yup, great !

Answer 14

How about a sum of the 24 terms ?

Answer 15

or no ?

Answer 16

Nah, we just had to find the 24th term c: THANKS!

Answer 17

\(\large\color{midnightblue}{ \rm S_{n}=\frac{1}{2}(a_1+a_n) \times n }\)

Answer 18

Okay, whatever ... yw !