Question

find the sum 26th term of an ap whose n term is 2n + 5

Answer 1

Tn = 2n+5

a = T1 = 2*1+5 = 2+5 = 7

l = T26 = 2*26+5 = 52+5 = 57

Sn = $\frac{n}{2}$[a+l] = $\frac{26}{2}$[7+57] = 13*64 = 832

Answer 2

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