Question

wykaż że jeśli x+y=-6 i x^2+y^2=27 to x*y=4,5

Answer 1

 

x + y = -6

x² + y² = 27

 

x+y = -6 | ()²

x² + 2xy + y² = 36

 

x² + 2xy + y² = 36

x² + y² = 27

---------------------- <-- odejmuję stronami

2xy = 9 |:2

xy = 4,5 c.k.d

 

 

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Pozdrawiam :)

Answer 2

x + y = -6

 

x² + y² = 27                              x² + y² = (x + y)² - 2xy

(x + y)² - 2xy = 27

 (-6)² - 2xy = 27

 36 - 2xy = 27

-2xy = 27 - 36

-2xy = - 9

 xy = 4,5       ---  odpowiedx