Question

Identify the 42nd term of an arithmetic sequence where a1 = -12 and a27 = 66

Answer 1

Solve them simultaneously,you will get two equations
Use elimination
Bingo :)

Answer 2

i have no clue what i'm even doing to eliminate :(

Answer 3

a27 = -12 + 26d = 66

Answer 4

find d

Answer 5

You are given with first term = -12 and a(27) = 66

So:

Use :
\[\large a_n = a + (n-1)d\]

So:

\[66 = -12 + (27-1)d \implies 66 = -12 +26d\]

\[d = \frac{78}{26} = 3\]

So now you have to find 42th terms:

So n= 42 a = -12 and d = 3

\[\large a_{42} = -12 + (42-1 ) (3)\]

Solve this now..

Answer 6

okay @Yahoo! , lets see .... 66+12=78, and 78/26 = 3?

Answer 7

yes go ahead..

Answer 8

ok now d = 3

follow watereyes

Answer 9

a42 = -12 + 41d

Answer 10

subs for d -12 + 41*3 =??

Answer 11

@waterineyes so then its.. 111?

Answer 12

-12 + 123 = 111

Answer 13

Let me check :

-12 + 41*3 = 123 -12 = 111

Yes you are right..

Well Done..

Answer 14

so thats ur 42 term

Answer 15

great ! thanks guys :)

Answer 16

Yahoo no need..