If the 7times the 7th term of an ap its equal to 11times the 11th term of an ap then find 18th term

If the 7times the 7th term of an ap its equal to 11times the 11th term

1.	If the 7times the 7th term of an ap its equal to 11times the 11th term of an ap then find 18th term
Answer» 7th term = (a+6d) 11th term = (a+10d)(a+6d)7 since 7th term of the ap is 7 times and the same for 11th term(a+6d)7=(A+10d)11 (given)7a + 42d =11a +110d (on solving)7a - 11a = 110d - 42d-4a = -68da= -17dwe know 18th term = (a+17d)................................. (i)now we substitute the value of a in (i) which emplies, -17d + 17d = 0