Mathematica DeMYSTiFied

¹Remember that the circle of radius r centered at the point (h, k) has equation (x−h)² +(y−k)² =r². Thus the circle with radius r = 2 and center (h, k) =(0, 0) has equation x² + y² = 4. The closed disk of all points inside the circle together with the circle itself would be given by the inequality x² + y² ≤ 4. If we replaced the less than or equal sign, ≤, with a strictly less than sign, <, we would then have the open disk consisting of only the points inside the circle.