Question

the sum of n terms of an ap is 5n square + 3 and if its a mth term is 168 find the value of M also find the 20th term of the AP

Answer 1

the sum of n terms=5n sq.+3

the sum of 1 term(a)=5*1*1+3=8

the sum of 2 terms=5*2*2+3=23

therefore,2nd term=23-8=15

d=15-8=7

Mth term=a-(M-1)d

             168 =8+(M-1)7

          168-8/7=M-1

       160/7+1=M

      22.8+1=M

M=23.8

Answer 2

There exists no value for m as it does not contain a pure value