👤

Daca x-y=4 si x²+y²=22,calculati xy

Răspuns :

ridicam prima ecuatie la patrat
(x-y)²=16
x² -2xy+y²=16
x²+y²-2xy=16
dar
x²+y²=22
deci
22-2xy=16
-2xy= -6
⇒ 2xy=6 ⇒ xy=3