Question

The 2nd term and its 4th term of an AP are 8 and 14 .Find the sum of the first 51 terms of the AP

Answer 1

a+d=8
a+13d=14
subtract
12d=6
d=1/2
a=8-1/2=15/2
sum of 51 terms
=(51/2)*(2(15/2) + 50(1/2))
(51/2)*(15+25)
=51*20
=1020