Maths

Plz the first and last term of an AP are 79 and -5 if the sum is 814. Find
A. The number of terms
B. Common difference.

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  1. http://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html

    XN = 79+d(N-1) = -5
    814 = N/2[ 2(79) + (N-1)d ]

    814 = N/2 [ 79 -5 ]

    N = 1628/74
    N= 22
    then
    -5 = 79 +d(21)
    d = -84/21 = - 4

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  2. where is the last answer

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