HellBender Posted December 5, 2003 Share Posted December 5, 2003 Wow, I totally forgot how to calculate the xth term of a series. Whats the formula again? Ex. First term of a series is -3 and each term after that is 5 more than the previous one (-3, 2, 7, 12...) What is the 101st term? Answer is 497. How? Link to comment Share on other sites More sharing options...
obiwong Posted December 6, 2003 Share Posted December 6, 2003 101 ∑ -3 + 2 + 7 + 12 + ... + 497 = i + (4i-8) i=1 i think... :huh: Link to comment Share on other sites More sharing options...
MDboyz Posted December 6, 2003 Share Posted December 6, 2003 J Wong.. I like the way you solve that... This is my way for that sort of problem. -3 , 2, 7, 12 , .... \ /\ /\ / 5 5 5 ----> 5x \/ \ / 1 1 the whole equation is 5x - c, when c = (2nd line #) - first initial number = 5 -(-3) = -8 ===> y = 5x - 8 I think ......!! :whistle: Link to comment Share on other sites More sharing options...
dreamz Veteran Posted December 6, 2003 Veteran Share Posted December 6, 2003 j wong and mdboyz are right, but it's not a sum. just do 5n - 8. you'll see it fits the series. so 101st term is 5*101 - 8 = 505 - 8 = 497. Link to comment Share on other sites More sharing options...
HellBender Posted December 6, 2003 Author Share Posted December 6, 2003 I went through my old notes.. It's this: the nth term = the first term + (n-1)® where r is whatever you're adding to get the next term (5 in this case). 497 = -3 + 100 (5) lol. thanks for the help though :p Link to comment Share on other sites More sharing options...
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