设复数z=-3cosθ+2isinθ (1)当θ=4/3π时,求|z|的值; (2)若复数z所对应的点在直线x+3y=0上,求2cos2θ2−12sin(θ+π4)的值.
问题描述:
设复数z=-3cosθ+2isinθ
(1)当θ=
π时,求|z|的值;4 3
(2)若复数z所对应的点在直线x+3y=0上,求
的值. 2cos2
−1θ 2
sin(θ+
2
)π 4
答
(1)∵θ=
π,∴z=−3cos4 3
π+2isin4 3
π=4 3
−3 2
i,∴|z|=
3
=
(
)2+(−3 2
)2
3
.
21
2
(2)由条件得,-3cosθ+3(2sinθ)=0,∴tanθ=
.1 2
原式=
=cosθ sinθ+cosθ
=1 tanθ+1
.2 3