x=cosa ,2y=sina
x²=cos²a,4y²=sin²a
x²+4y²=cos²a+sin²a=1
x+y=1,x=1-y
(1-y)²+4y²=1
5y²-2y=0
y(5y-2)=0
y1=0,y2=2/5
x1=1,x2=3/5