[size=150][color=#0000ff]Circle is the locus of a point which moves such that its distance from a fixed point is constant.[br]The fixed point is called the centre of the circle and the distance of any point on the circle from[br]the centre is called the radius of the circle.[/color][br]Let [math]\left(h,k\right)[/math] be the centre of the circle and let [math]P\left(x,y\right)[/math] be any point on the circle with radius [math]a[/math]. Then we have [br][math]\sqrt{\left(x-h\right)^2+\left(y-k\right)^2}=a[/math] or [math]\left(x-h\right)^2+\left(y-k\right)^2=a^2[/math]. [br]In the applet below drag the centre C or change the coordinates of Centre in the input box . Similarly change the radius in the input box or by the slider. Observe the changes in its equation. For answering the questions use the applet.[/size]

To answer the following questions you may drag the centre C in the above applet to appropriate positions and use the radius slider or you may use the input boxes straight away.