x+2y=1
x=1-2y
x^2+y^2
=(1-2y)^2+y^2
=1-4y-4y^2+y^2
=5y^2-4y-1
=5(y^2-4y/5)-1
=5(y^2-4y/5+4/25)-1-4/5
=5(y-2/5)^2-9/5
x,y>=0
x=1-2y>0
y>0
0=