Mathematics : Arithmetic Sequence

The 5th term and the 8th term of an arithmetic sequence are 18 and 27 respctively.
a)Find the 1st term and the common difference of the arithmetic sequence.
b)Find the general term of the arithmetic sequence.

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  1. an = a1 + (n-1)d
    18 = a1 + (5-1)d
    27 = a1 + (8-1)d
    so
    -9 = -3d
    d = 3
    then a1 = 18 - 12 = 6
    so
    an = 6 + (n-1)3

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  2. common difference=3,1st term=6and general term=3+3n

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  3. 13,26,39,52

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