(1+3√2)(3√2-1)=(3√2+1)(3√2-1)=(3√2)²-1²=9·2-1=17
(5√2+3)(3-5√2)=(3+5√2)(3-5√2)=3²-(5√2)²=9-25*2=-41
X+y=20
x*y=75
x=20-y
(20-y)y=75
20y-y^2=75
-y^2+20y-75=0 /-1
y^2-20y+75=0
D= 400-300=100
y1=20+10/2=15
y2=20-10/2=5
x=20-y
x1=20-15=5
x2=20-5=15
x1=5; y1=15
x2=15; y2=5