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katiebugg

  • 3 years ago

The third term of an arithmetic sequence is 9 and the seventh term is 31. Find the sum of the first twenty-two terms.

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  1. helder_edwin
    • 3 years ago
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    an arithmetic sequence is of the form \[ \large a_1\qquad\text{not given} \] \[ \large a_2=a_1+d \] \[ \large 9=a_3=a_2+d=a_1+2d \] so \[ \large 31=a_7=a_1+6d \]

  2. helder_edwin
    • 3 years ago
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    u end up with \[ \large 9=a_1+2d \] \[ \large 31=a_1+6d \] solve this system

  3. helder_edwin
    • 3 years ago
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    r u there @katiebugg ?

  4. katiebugg
    • 3 years ago
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    sorry yeahh was working on a prob thanks!!!

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