Question

已知(x²+y²)(x²+y²-1)=6,求x²+y²的值

Answer 1

(x²+y²)(x²+y²-1)=6

(x²+y²)²-(x²+y²)-6=0

(x²+y²-3)(x²+y²+2)=0

x²+y²=3 或x²+y²=-2(舍)

x²+y²=3

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