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问题: 复平面上的图形

Z^2 +49/Z^2 是实数,
求Z在复平面上的图形

解答:

设Z=x+yi ,(x,y∈R, xy不同时为0)
(x+yi)²+49/(x+yi)²
=(x²-y²)+2xyi +49/[(x²-y²)+2xyi]......(1)

49/[(x²-y²)+2xyi]
=49(x²-y²)/(x²-y²)² -98xy/(x²+y²)²i
==>
(1)=(x²-y²)+49(x²-y²)/(x²-y²)² +[2xy -98xy/(x²+y²)²]i

是实数
2xy -98xy/(x²+y²)² =0
==>
x=0或y=0 ,或x²+y²=7
表示X,Y轴不包括原点,以及圆x²+y²=7