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Math Help - sequences

  1. #1
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    sequences

    I was given this question and don't really know where to start, any help would be much appreciated..

    "If the sequence a is arithmetic, and a_3 = 5, and a_5 = 15, find a_9"

    Is the awnser 35?
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    Quote Originally Posted by 14041471 View Post
    I was given this question and don't really know where to start, any help would be much appreciated..

    "If the sequence a is arithmetic, and a_3 = 5, and a_5 = 15, find a_9"

    Is the awnser 35?
    Yes
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  3. #3
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    Quote Originally Posted by 14041471 View Post
    "If the sequence a is arithmetic, and a_3 = 5, and a_5 = 15, find a_9"
    If the sequence is arithmetic, then the same amount "d" is added at each stage. Then a_4 = 5 + d and a_5 = a_4 + d = (5 + d) + d = 5 + 2d = 15. Then 2d = 10, so d = 5.

    Quote Originally Posted by 14041471 View Post
    Is the awnser 35?
    Yup!
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