Algebra 1a

Question

Tell whether the sequence is arithmetic. If it is, what is the common difference? 

-15.-9.-3.3....

a. yes;3

b. yes;5

c.yes;6

d. no 

Answer 1

No you don't subtract 3 from -15.

You find what the difference between -15 and -9 is, which is written as:

|-15 -(-9)| : absolute value

|-15 + 9|

|-6|

6 is the difference

Check the next number:

|-9 -(-3)|

|-9 + 3|

|-6|

6

Same difference, so it is an arithmetic sequence and the common difference is 6

Just to check the last number:

|-3 -(+3)|

|-3 - 3|

|-6|

6 : check

 

Answer 2

 

-9-(-15) = 6

-3-(-9) = 6

3-)-3) = 6

 

Difference between terms is 6

Answer 3

An arithmetic sequence is one where the difference between each number and the one before it is the same.  Or to put it another way, the number increases by the same amount in each step.

 

Is that the case here?  Subtract each number from the one before it and see what you get.  Then you'll see the answer easily.