x^2+4y^2+4xy=1
4(x^2+y^2)=1-4xy+3x^2
=1+3x^2-2x(1-x)
=1+5x^2-2x
=1+5x^2-2x
=5(x^2-2x/5+1/25)+1-1/5
=5(x-1/5)^2+4/5
(x^2+y^2)=5(x^2-1/5)^2/4+1/5
0<=x<=1
最大值：(16*5)/(25*4）+1/5=1
最小值：(x=1/5时), 1/5