Question

If 7 times the 7th term of an A.P. is equal to 11 times the 11th term ,then its 18th term​

Answer 1

7th term = a + 6d

11th term = a + 10d

= > 7×(a + 6d ) = 11 × ( a + 10d )

= > 7a + 42d = 11a + 110d

= > 7a - 11a = 110d - 42d

= > - 4a = 68d

$= > - a = \frac{68d}{4}$

$= > a = - 17d$

to find 18th term of AP

$= > a + 17d$

$= > - 17d + 17d$

$= 0$

The 18th term is 0