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The 4th term of an AP …

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The 4th term of an AP is OK. Prove that the 25th term of the AP is 3 times its 11th term.
  • 1 answers

Gaurav Seth 6 years, 8 months ago

We have given that
4th term of an A.P.= a4 = 0
∴ a + (4 – 1)d = 0
∴ a + 3d = 0
∴ a = –3d        ….(1)

25th term of an A.P. = a25
= a + (25 – 1)d
= –3d + 24d      ….[From the equation (1)]
= 21d

3 times 11th term of an A.P. = 3a11
= 3[a + (11 – 1)d]
= 3[a + 10d]
= 3[–3d + 10d]
= 3 × 7d
= 21d

∴ a25 = 3a11

i.e., the 25th term of the A.P. is three times its 11th term.

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