# What is the sequence formula?

• Apr 20th 2010, 04:57 PM
meggnog
What is the sequence formula?
3, -4, 7, -12, 19, ...

What is the next number in the sequence? What is the formula for the nth term of the sequence?

• Apr 20th 2010, 05:05 PM
-28

Will think of definite formula for nth term. Hold on.
• Apr 20th 2010, 05:08 PM
pickslides
Quote:

Originally Posted by meggnog
3, -4, 7, -12, 19, ...

What is the next number in the sequence? What is the formula for the nth term of the sequence?

Hi there, consider the following.

The absolute differences from each term follows a pattern \$\displaystyle 1,3,5,7,\dots \$

Every the sign of every second term alternates. And looking at the differences after breaking the patterns into positive and negative numbers you get are \$\displaystyle 4,8,12,\dots\$

Spoiler:
The next term is \$\displaystyle -28\$
• Apr 20th 2010, 05:12 PM
Quote:

Originally Posted by pickslides
Hi there, consider the following.

The absolute differences from each term follows a pattern \$\displaystyle 1,3,5,7,\dots \$

Every the sign of every second term alternates. And looking at the differences after breaking the patterns into positive and negative numbers you get are \$\displaystyle 4,8,12,\dots\$

Spoiler:
The next term is \$\displaystyle -28\$

Is there a formula to generate arithmetic sequences? I think it's usually recurrence relationships but maybe you can see something...

Difference between |nth| term and |(n-1)th| term is 2n-3...