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2 March, 06:55

The third and thirtieth term of an arithmetic sequence are 4 and 85 write an explicit rule for this sequence

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  1. 2 March, 10:33
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    An=a1+d (n-1)

    a3=4=a1+d (3-1) = a1+2d

    a30=85=a1+d (30-1) = a1+29d

    4=a1+2d

    85=a1+29d

    85-4 = (a1+29d) - (a1+2d) =

    81=a1-a1+29d-2d=27d

    81=27d

    divide both sides by 27

    3=d

    4=a1+3 (2)

    4=a1+6

    minus 6

    -2=a1

    an=-2+3 (n-1)

    an=-2+3n-3

    an=-5+3n
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