Question

of the second term and the fourth term of an A.P.are 12 and 20 respectively, then find sum of first 25 term​

Answer 1

hey mate here is your answer.

let first term=a

common difference=d

a/q

n12=a+11d

12=a+11d (eq.1st)

n20=a+19d

20=a+19d (eq.2nd)

eq.2-eq.1

we get,

8=8d

d=1

therefore a=1

sum of first 25th term = 25/2×(2a+(n-1)d)

on putting the value we get,

25/2 ×26

=25×13

i.e 325

hope it helps ####