arithmetic

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the first and second terms of an arithmetic progression are 161 and 154 respectively.the sumthe first m terms is zero.find the value of m

  • arithmetic -

    a = 161
    a+d = 154 , so d = -7

    S(m) = (m/2)(2a + (m-1)d)
    0 = m/2(322 - 7m+ 7)
    329m - 7m^2=0
    49m - m^2 = 0
    m(49-m)=0
    m = 49

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