Question

find sum of 50 terms of ap whose second and thirs terms are 14 and 18

Answer 1

hope it may help you

Answer 2

an = a+(n-1)d
so, 2nd term = a+( 1-1)d=14
= a+d=14
3rd term = a +(3-1)d=18
= a+ 2d
substitute u would get
d=4 and a=10
sn=n/2 (2a+(n-1)d)
substitute u would get
answer =90