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Find the 10th term from the end of the AP 4, 9, 14, … … … . , 254. |
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Answer» Given, AP is 4, 9, 17……...,254. First term of AP is a = 4. Common difference of AP is d = a2 – a1 = 9 – 4 = 5. nth term of AP is an = 254. ∵ an = a + (n – 1) d ∴ a + (n – 1) d = 254 ⇒ 4 + (n − 1)5 = 254 (a = 4 & d = 5 and an = 254) ⇒ 5(n − 1) = 254 − 4 = 250 ⇒ n − 1 = \(\frac{250}{5}\) = 50 ⇒ n = 50 + 1 = 51. 10th term from the end of the AP is 51 – (10 – 1) = 51– 9 = 42th term of AP. ∴ a42 = a + (42 – 1)d = 4 + 41 × 5 = 4 + 205 = 209. (∵a = 4,d = 5) Hence, The 10th term from the end of the given AP is 209. |
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