Which of the following subsets of R2\mathbb{R}^2R2 is a subspace?
{(x,y):x+y=1}\{(x, y) : x + y = 1\}{(x,y):x+y=1}
{(x,y):x2+y2=1}\{(x, y) : x^2 + y^2 = 1\}{(x,y):x2+y2=1} (unit circle)
{(x,y):2x−3y=0}\{(x, y) : 2x - 3y = 0\}{(x,y):2x−3y=0}
{(x,y):x≥0}\{(x, y) : x \geq 0\}{(x,y):x≥0}