Circle
1. When the center of circle is origin.→x2+y2 = r22. When the center of circle is (h, k).→(x-h)2+(y-k)2 = r2 ..................(i)3. When the circle touches x-axis.If the circle touches x-axis then...
Equation of Circle in Diameter form
Let AB the diameter of the circle with center O where A(x1, y1) and B(x2, y2) are the end-points of the diameter.
Let P be any point on the circumference of the circle. Then, AP and BP is joined such that triangle ABP is formed as shown in the figure.
Then,
angle APB = 90O [angle at semi-circle is right angle]