Question

Find the next two terms of the following sequence:

-21. -9, 11, 39

Answer 1

F(1) = -21

F(2) = -9 = -21 + 4 x 3 = F(1) + 4 x (2^2 - 1)

F(3) = 11 = -21 + 4 x 8 = F(1) + 4 x (3^2 - 1)

F(4) = 39 = -21 + 4 x 15 = F(1) + 4 x (4^2 - 1)

...

F(n) = F(1) + 4 x (n^2 - 1)

=> F(5) = -21 + 4 x (5^2 - 1 ) = -21 + 4 x 24 = 75

=> F(6) = -21 + 4 x (6^2 - 1) = -21 + 4 x 35 = 119

Hope this helps!

:)

Answer 2

Answer:You're adding 7 each time (18 - 11 = 7, 25-18 = 7, etc etc)

Rule:

(nth term) = (previous term) + 7

a%5Bn%5D+=+a%5Bn-1%5D%2B7

The recursive rule is a%5Bn%5D+=+a%5Bn-1%5D%2B7

3x-x+2=4 ...

Explanation: