St charles

The third term of an A.P is 8 and 9th term of the A.P.exceeds three times the third term by 2.find the sum of its first 19th terms.

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  1. a+2d = 8
    a+8d = 3(a+2d)+2 = 26

    so, 6d = 18, and d=3

    Now you can find a, and answer the question.

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  2. a= 2
    S19=551

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  3. a+2d=8
    a+8d=3(a+2d)+2=26
    6d=18
    d=6
    put d in a+2d= 8
    a+2(3)=8
    a+6=8
    a=8-2
    a=2
    Sn= n/2[2a+(n-1)d]
    =n/2[2(2)+(n-1)3]
    n/2[4+3n-3]
    2n+3n-3
    5n+3
    n=5/3

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  4. how in first 26 came, sir pls..can u explain me....

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  5. sir pls can u tell me in first how 26 came...?

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  6. how 26 came ??

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