Math Help - simple sequence question

1. simple sequence question

Determine the tenth number in each number pattern:

a) 12,3,-6....
b) -18,-7,4...

is there any other way to get the 10th term rather than just keep going till i reach the 10th number?

thankies

2. Try $a_{n}=a_{1}+(n-1)d$

$a_{1}$ is the first term.

d=common difference.

n=the nth term you want

Try #1 for the 10th term:

$12+(10-1)(-9)=-69$

Now, try the 2nd one yourself. OK?.

3. thanx a lot!