Question

7 times the 7th term of an ap is equal to 8 times its 8th term, show that its 15th term is 0

Answer 1

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 = -68d

a= -17d

we know 18th term = (a+17d)................................. (i)

now we substitute the value of a in (i)

which emplies,

-17d + 17d

= 0

hence prove..