Question

The 24th term of an AP is twice its 10th term. Show that its 72nd term is 4 times its 15th term.

Answer 1

`T_(24) = 2T_(10) rArr a + 23d = 2 (a+9d) rArr a -5d = 0 rArr a = 5d. " "..(i)`
`T_(72) = a +71d = 5d + 71d = 76d.`
`T_(15) = a +14d = 5d + 14d = 19d.`
Hence, `T_(72) = 4 xx T_(15).`