Question

若实数x，y满足(x²+y²)²-5(x²+y²)-6＝0，则x²+y²的值为

1. A.
   6
2. B.
   -1
3. C.
   6或-1
4. D.
   -6或1

Answer 1

A
(x²+y²-6)(x²+y²+1)＝0，因为x²+y²+1＞0，所以x²+y²＝6