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2. 解:(1)原式=

　　　　　 =0

1. 解：原式＝2+1－9+1 ···························································································· 4分

　　　　　　 ＝－5　　 6分

65. ；66. 1.56×10⁹

59. 10³　 　60. －5；61. ；62.6；63. ；64. 1.58×10¹¹

57.6； 58. 6.80×10⁸

56. 9.1×10⁴

50. ；51. ；52. ；53. 2008；54. ；55. 15℃

44. 6.8× 10⁸ 　45.5；46. ；47.2；48. ；49. 3；1；

42. ；43.

38. ；39.1；40. -6；41.