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Given that 1st term of an A.P is 7 and it's 10th term is twice the second term,calculate the (a) 19th term (b)sum of 28 terms (c) difference between 9th and 6th terms

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  • Community technical college -

    a10=a1+r(10-1)
    14=7+r(9)
    r=7/9
    check
    7, 7 7/9, 7 14/9, 7 21/9, 7 28/9, 7 35/9, 7 42/9, 7 49/9, 7 56/9, 14

    Use the formulas for sum, knowing r, a1

  • King george memorial college (Ilado Badagry Lagos state) -

    1st term=7 2nd term=a+d
    10term=a+9d
    7+9d=2(14+2d)
    14-7=9d-2d
    7=7d=d=1
    sum of 28 term
    n/2(2a+(n-1)d)
    28/2(2*7+(28-1)1)
    14(14+27)=14(41)
    25term=574
    9th term=7+(9-1)1
    7+(9-1)
    7+8=15
    6th term=7+(6-1)1
    7+(6-1)=7+5=12
    9th term-6th term=15-12=3.

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