Question

If the sum of first k terms of an A.P. is 3k2-k and its common difference is 3, what is the
first term?

Answer 1

Answer:

2

Step-by-step explanation:

S(k)= 3k^2-k
S(k-1) = 3(k-1)^2 -(k-1)

a(k)= S(k)-S(k-1)
a(k) = 3k^2-k - {3(k^2+1-2k) -k+1}
a(k) = 3k^2-k - {3k^2+3-6k) -k+1}

a(k) = 3k^2-k - 3k^2-3+6k +k-1
a(k) =  -3+6k -1 = 6k-4
a(1) = 6(1)-4= 6-4=2
∴First term = 2.



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