Given, r = {7, -20, 61...} Find a relationship between the first three terms of the sequence: The difference between 7 and -20 is <span>(−3<span>)3</span>=−27</span> The difference between -20 and 61 is <span>(−3<span>)4</span>=81</span> Thus we can assume the next term of the sequence is <span>61+(−3<span>)5</span>=61−243=−182</span> If <span>−182</span> is the next term of the sequence, then term following it is: <span>−182+((−3<span>)6</span>=−182+729=549</span> And the term following 549 is <span>549+(−3<span>)7</span>=549−2187=−1638</span> In other words, the common difference between the terms is <span>(−3<span>)<span>n+2</span></span></span> Which is neither arithmetic nor geometric
