What is the equation of a circle that has radius #r# centred on the origin?

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Answer 1 · 2017-07-06T17:11:40

# x^2 + y^2 = r^2 #

The standard equation of a circle with centre #(a,b)# and radius #r# is:

# (x-a)^2 + (y-b)^2 = r^2 #

Thus the equation we seek with centre #(a,b)=(0,0)# is:

# (x-0)^2 + (y-0)^2 = r^2 #

i.e.

# x^2 + y^2 = r^2 #