中四-數學 MC【20點】

10.
答案是： C.-16i

64i^5 ÷ 4i^2
= 16i^(5-2)
= 16i^3
= 16(-i)
= -16i


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11.
答案是： C.-√39


√(-13) x √(-3)
= (√13)i x (√3)i
= (√39)i^2
= (√39) x (-1)
= -√39


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12.
答案是： B.8

(2 + 3i)(6 - 5i)
= 2(6 - 5i) + 3i(6 - 5i)
= 12 - 10i + 18i - 15i^2
= 12 + 8i + 15
= 27 + 8i


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13.
答案是： B.8/113

1 / (8 - 7i)
= (8 + 7i) / (8 - 7i)(8 + 7i)
= (8 + 7i) / [8^2 - (7i)^2]
= (8 + 7i) / (64 + 49)
= (8 + 7i) / 113
= (8/113) + (7/113)i


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14.
答案是： B.-5 + 10i


-5 - 10i 的共軛複數
= -5 - (-10i)
= -5 + 10i


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15.
答案是： D.7 - 9i

(4 - 5i) - (-2 + 3i) + (1 - i)
= 4 - 5i + 2 - 3i + 1 - i
= (4 + 2 + 1) + (-5 - 3 - 1)i
= 7 - 9i