Question 818958
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Hi,
Standard Form of an Equation of a Circle is {{{(x-h)^2 + (y-k)^2 = r^2}}} 
where Pt(h,k) is the center and r is the radius
9x^2+9^y2-441 = 0  |Note the use of ^ (upper case 6)
9x^2+9y^2 = 441    |dividing each term on both sides of the EQ by 9
 {{{x^2 + y^2 = 49}}}   r = 7