✔ 最佳答案
(a) (6 + 3i) / 15
= 6/15 + 3i/15
= 2/5 + i/5
(b) (4 + i) / (3 - i)
= (4 + i)(3 + i)/(9 + 1)
= (12 - 1 + 7i)/10
= 11/10 + 7i/10
(c) (- 6 + i) / (2i - 3)
= (-6 + i)(-3 - 2i)/(9 + 4)
= (18 + 2 + 9i)/13
= 20/13 + 9i/13
(d) 3(4 + i ) / (3 + 2i)
= 3(4 + i)(3 - 2i)/(9 + 4)
= 3(12 + 2 - 5i)/13
= 42/13 - 15i/13
(e) (4 + i)/(5 - i) + (4 - i)/(5 + i)
= (4 + i)(5 + i)/(25 + 1) + (4 - i)(5 - i)/(25 + 1)
= (20 -1 + 9i + 20 - 1 - 9i)/26
= 38/26
= 19/13
15. 計算下列各式 , 並把結果寫成 a + bi 的形式。
(a) (1 + 3 i ) (3 + 2 i) - (4 + 3 i)
= 3 - 6 + 9i + 2i - 4 - 3i
= -7 + 8i
(b) 1 / (2 - 5 i) ^ 2
= 1 / (4 - 20i - 25)
= -1/(19 + 20i)
= -(19 - 20i)/(361+400)
= (-19 + 20i)/761
= -19/761 + 20i/761
(c) 4 ( - 2 + 3 i) / (2 i - 3 )
= 4(-2 + 3i)(-3 - 2i)/(9 + 4)
= 4(6 + 6 -9i + 4i)/13
= 4(12 - 5i)/13
= 48/13 - 20i/13
(d) (3 + i) ^ 3
= 27 + 3*9i + 3*3i^2 + i^3
= 27 + 27i - 9 - i
= 18 + 26i