Question

Find the sum of first 10 terms of an a.p In which 3rd term is 7 and 7th term is two more than thrice of its third term

Answer 1

Step-by-step explanation:

let

first term=a

common difference=d

nthterm=a+(n-1)d

3rd term=a+2d=7----------(1)

7th term=a+6d=3(3rd term)+2=23----------(2)

solve (1)and(2)

d=4

a=-1

sum of n terms=n/2[2a+(n-1)d]

sum of 10 terms=10/2[2(-1)+(10-1)4]

=5[-2+36]

=5(34)=170.