What is the equation of a circle with centre of origin and radius is 6 cm?

$x^2 + y^2 - 36 = 0$

We know that,

(x - x₁)² + (y - y₁)² = r² 

Radius of circle = 6 cm

Here,

x₁, y₁ = the center of the circle

c = radius of the circle

The center is at the origin

So here, x₁ = 0, y₁ = 0

Radius of the circle (c) = 6 cm

Equation of circle is = (x - 0)² + (y - 0)² = 6²  

= x² + y² - 36 = 0