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Aflati x-y si xy stiind ca x² + y²=21 si x+y = 5

Răspuns :

x²+y²=21
x+y=5
x²+2xy+y²=25
21+2xy=25
2xy=4
xy=2
x²+y²-2xy=21-2×2=17
(x-y)²=17
x-y=√17