The standard form of the equation of a circle is:

Where the point (a,b) represents the centre and r is the radius. So, given your information, the equation will be:
A(10) = <span>9(10) + 9= 90+9 =99
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Change 4/5 - 2/3 so that the denominator is th same. Let’s try 15.
So, 12/15 - 10/15.
Then, subtract to get 2/15.
Hope it helped :)