Which sequence is an example of an arithmetic sequence

Only the third sequence is arithmetic

Step-by-step explanation:

If the sequence has a common difference, then it is arithmetic.  To find the common difference, substract a term from the next term.

First sequence:  

10 - 20 = -10     5 - 10 = -5    The differences are not the same,   so the sequence is NOT arithmetic

Second sequence:

-6 - (-3) = -3     -18 - (-6) = -12   The differences are not the same,   so the sequence is NOT arithmetic

Third sequence:

 10 -  5 =  5     15 - 10 = 5   20 - 15 = 5  The differences are the same,   so the sequence is arithmetic

Fourth sequence:

10 - 5 = 5    20 - 10 = 10   The differences are not the same,   so the sequence is NOT arithmetic

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answer

answer: they are supplementary angles

step-by-step explanation: 161+19=180. supplementary angles equal 180 degrees