Question

if 7 time the 7th term of an AP is equal to 11 time its 11th term, show that the 18 th term

Answer 1

we know seventh term,=a+6d and 11th tern =a+10d ...so,
7(a+6d)=11(a+10d)
42d-110d=11a-7a
5a=-68d
Now 18th term =a+17d
put a=(-68/5)d in the above statement.. u will get ans