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5+(-41)+9+(-39)+13+(-37)+17.....+(-5)+81+(-3) |
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Answer» Nice ? Well, don\'t mind.... but may i know, from where you got this question ???Well, the answer will be :-The given series is 5+(-41)+9+(-39)+..+(-5)+81+(-3).This is consisting of two AP\'s.S1=5+9+13+....+77+81, where a=5, d=4S2=−41−39−37−...(−3), where a=−41 and d=2for S1, 81=5+(n−1)×4 ⇒ n−1 =764, hence n=20S20\xa0= 202×[5+81]=10×86 = 860 for S2, −3 = −41+(n−1)×2 ⇒ n−1 = 382,Hence,\xa0n=20S20\xa0= 202×[−41−3] = −10×44 = −440Total sum=S1+S2\xa0= 860−440 = 420Therefore, Answer = 420. |
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