1.

Find the value of a25 - a15 for the AP: 6, 9, 12, 15, ………..ORIf 7 times the seventh term of the AP is equal to 5 times the fifth term, then find the value of its 12th term.

Answer»

a = 6, d = 3 ; a25 = 6 + 24(3) = 78

a15 = 6 + 14(3) = 48 ; a25 - a15 = 78 - 48 = 30

OR

7(a + 6d) = 5(a + 4d)

⇒ 2a + 22d = 0

⇒ a + 11d = 0

⇒ t12 = 0



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