ASTROID

 

This astroid is the set of points (x,y)∈R2(x,y)∈R2 such that

|x|23+|y|23−1.8=0,−3≤x≤3, −3≤y≤3.|x|23+|y|23−1.8=0,−3≤x≤3, −3≤y≤3.

generated with pstricks