x^2+y^2=1
x^2+y^2=16
y=5x+1/2
x^2+9y^2=9
y=x/5-7
25x^2+9y^2=225
y=4x^2+3
y=x^2
y=-3x-2
x^2+y^2=81
x^2+y^2=36
4x^2+36y^2=144
y=-1/2x+4
y=x^2-1
5x^2+2y^2=10
y=-2x^2
