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Val97

  • 3 years ago

Please Help! Show me how its done please! Find the sum of the first 8 terms of the sequence. 1, -3, -7, -11, ...

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  1. amistre64
    • 3 years ago
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    sooo, you need help adding? or is it that you really need help in determining all the 8 terms?

  2. amistre64
    • 3 years ago
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    since the numbers are getting smaller, or going negative, ... and they seem fairly close together. We can try to see if they are subtracting a like amount each time.

  3. Notamathgenius
    • 3 years ago
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    Fine out what the term is going up by. I see -4

  4. Val97
    • 3 years ago
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    I need help determining all the 8 terms, this is pre cal and it really confuses me. I'm not sure what formula to use. The Arithmetic Sequence formula?

  5. amistre64
    • 3 years ago
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    formulas are only half the battle. seeing a pattern is the key once you see that pattern, the formula is known by default

  6. Val97
    • 3 years ago
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    So that is it? Its isn't any of the formulas they gave me?

  7. amistre64
    • 3 years ago
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    if you subtract 4 from the last term given, what do you get?

  8. Val97
    • 3 years ago
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    -15, -19, -23

  9. amistre64
    • 3 years ago
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    .... or if you want to create an expression to use in summation thats fine too \[\sum_{n=a}^b~a_1+d(n-1)\] \[\sum_{n=a}^b~a_1+\sum_{n=a}^bd(n-1)\] \[a_1(b-a)+d\sum_{n=a}^bn-1\] \[a_1(b-a)+d\sum_{n=a}^bn-d\sum_{n=a}^b1\] \[a_1(b-a)+d\sum_{n=a}^bn-d(b-a)\] stuff like that

  10. amistre64
    • 3 years ago
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    but yes ..., -15, -19, -23, -27 fill in all 8 terms

  11. amistre64
    • 3 years ago
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    \[\frac{n}{2}(a_1+a_8)=sum\]

  12. Val97
    • 3 years ago
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    ok got it! thanks!

  13. amistre64
    • 3 years ago
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    youre welcome, good luck :)

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