FInd the sum of the first eight terms of a linear sequence whose first term is 6 and whose last term is 46
we don't know how many terms, we don't know the common difference
we know:
a = 6
term(n) = a + (n-1)d
46 = 6 + nd - d
40 = d(n-1)
sum(8) = 4(2a + (7)d )
= 8a + 4(7)d
= 48 + 28d