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Daca x+y=2 si xy=-15, determinati numerele.

Răspuns :

x=-15y -15y+y=2 -14y=2 y=-7 x=9
x=2-y
(2-y)*y=-15
2y-y²=-15
y²-2y-15=0
Δ=4-4*1*(-15)=4+60=64
√Δ=+8 sau -8
y1=(2+8)/2=10/2=5
y2=(2-8)/2=-6/2=-3
x+5=2⇒x1=-3
x-3=2⇒x2=5