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Unformatted text preview: 89701 2000á / bª · l èÑk EJ ËF @O 7A 9 n a (n>2)èÑk· ª ·l á/ ª · l/ á bª al y ·á bª +1á / a·l a+2á / …· ª na a+(n− 8 1) a + ( a + 1) + (a + 2) + + (a + n − 1) = 2000 ⇒ n ⋅ [ 2a + ( n − 1) ] = 2000 2 ----------(1) 2a+n− 1 ⇒ n ⋅ (2a + n − 1) = 4000 = 2 5 × 5 3 8 2al øà ª· 8 8 n a 2a+n− 1 n a (2a− 1>0)8 c\ (1)˜· ˆ ¹ A ª{ • l á Ñb kÑè (A) 2a + n − 1 = 5 3 n = 25 (B) 2a + n − 1 = 5 × 2 5 n = 52 47,48,49,……,78 68,69,70,……,92 398,399,400,401,402 n=5 (C) 2a + n − 1 = 5 2 × 2 5 8 (A)ø à 8 (B)ø à 8 (C)ø à n=32 8 n=25 8 n=5 8 (a=47) (a=68) (a=398) ª·làø 81 ¶ ¹ b{ ª · c\ l 8á¹A• 2˜ ˆ Ñ ·kÑè 8 89702 8 O-ABC• c \¹ Ð O C A B BC = a, OA = a ′, AC = b, OB = b ′, AB = c, OC = c ′, a+a/8 b+b/8 c\ +¹c/Еc ª · øëlb ˆ\ ∆ABC , ∆OBC , ∆OAB , ∆OACª l øë·* l·ª \ ¹ • Ñ€ ˆ á ˜+ \ +Ð ¹• a <b+c a ′ < b′ + c′ 8 (1)+(2)ø -------(1) -------(2) ------- (3) ------- (4) a + a ′ < (b + b′)...
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