B) 0,5x-3,4(5-y)=4,7
x/2-17-3,4y=4,7
x-17-3,4y=9,4
x-3,4y=26,4
x-y=26,4/3,4
x=26,4/3,4 -y
y=26,4/3,4 -x
-4x+8y=12 | :-4
x+8y= -3
x+y= -3/8
x= -3/8 -y
y= -3/8 -x
X={-3/8 -y , 26,4/3,4 -y}
Y={-3/8 -x , 26,4/3,4 -x}
E) 3x-rad5y=2rad5
3x-rad5y=rad20
3x=rad25y
3x=5rady
(3x)^2 = (5rady)^2
9x^2 = 25y
x^2 = 25y/9
x= rad25y/9
x=5rady/3
y=5radx/3
7x-y=10
x-y=10/7
x=10/7 -y
y=10/7 -x
X={5rady/3 , 10/7 -y}
Y={5radx/3 , 10/7 -x}
Succes! :)