x^2 +y^2 -2xy =7+4=11=(x-y)^2 => x-y=√11 orx-y=-√11x^2 +y^2 +2xy =7-4=5=(x+y)^2 => x+y=√5or x+y=-√5四组 x-y=√11 ; x+y=√5 , x-y=√11 ; x+y=-√5 , x-y=-√11 ; x+y=√5 , x-y=-√11 ; x+y=-√5=> (x,y)=( (√11+√5)/2 ,(√5 -√11)/2 ) ; ( (√11-√5)/2 ,(-√5 -√11)/2 ) ;( (-√11+√5)/2 ,(√5 +√11)/2 ) ;
( (√5-√11)/2 ,(-√5 +√1...
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