Question

find the sum of first 10 terms of an AP 2, 7, 12...

Answer 1

here, a= 2, d=7-2=5, n=10
we know that,
Sn= n/2{2a+(n-1)d}
=10/2{2×2+(10-1)5}
=5(4+45)
=5×49
=245

Answer 2

answer is 245, bu using the formula
s= n/2(2a+(n-1)d)
where n the no of terms, a is the first number and d is the common difference