Family of Concentric Circles (circles having same center point, but different radii).
The equation that satisfies the family of concentric circles:
x² + y² = r²
Differentiate x² + y² =r²
[tex]2x + 2y \frac{dy}{dx}= 0 [/tex]
[tex]x + y \frac{dy}{dx} =0[/tex]