Respostas

  • Usuário do Brainly
2014-06-08T00:40:03-03:00
2x-y=11
xy=21
isolando  x=21/y

substituindo
2(21/y) -y =11
42/y -y =11
mmc=y
42 -y² =11y
-y² -11y +42=0
y² +11y =42=0
Δ=121+168=289     
√Δ=17
y=( -11 +17)/2= 6/2 =3
y = (-11-17)/2= -28/2= -14
 
sendo x=21/y
p/ y=3⇒x=21/3 =7
p/y= -14⇒ x=21/-14=-3/2
S={(7,3),(-3/2,-14)}

b)  x² +2y=20
     2x -y =-10          isolando  -y= -10 -2x
                                             y=10 +2x

x² +2(10+2x)=20
x² +20 +4x=20
x² +4x =0
x(x+4)=0
x=0
x+4=0⇒x=-4

sendo y=10+2x
p/x=0⇒y=10
p/x=-4⇒ y=10+2(-4)=10-8=2
S{(0,10),(-4,2)}
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