x*y=99
x-y=2
x=2+y
→y(2+y)=99
2y+y²=99
Primim ecuatia de gradul ll (ax²+bx+c=0) :
→y²+2y-99=0
a=1
b=2
c=-99
∆=b²-4ac=2²-4•1*(-99)=4+396=400
∆=400
y1;2= (-b±√∆)/2a
y1;2=(-2±√400)/2•1=(-2±20)/2
y1=(-2+20)/2=18/2=9
y2=(-2-20)/2=-22/2=-11 (nu corespunde, -11 nu apartine N)
→y=9
→x=2+9=11
_______________________
11*9=99
11-9=2
