Sample quiz on equation of a circle
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1. If the equation of a circle is given as $x^2+y^2=r^2$, the center of the circle is located at $\cdots$?
   
   $(r,r)$
   $(r,0)$
   $(0,0)$
   $(0,r)$
2. What is the radius of a circle whose equation is given by $x^2+y^2=9$?
   
   $3$
   $9$
   $27$
   $81$
3. What is the radius of a circle whose equation is given by $x^2+y^2=2$?
   
   $\sqrt{2}$
   $2$
   $4$
   $8$
   
4. Find the coordinates of the center of a circle whose equation is $x^2+(y-1)^2=10$
   
   $(0,0)$
   $(0,1)$
   $(1,0)$
   $(1,1)$
5. Find the coordinates of the center of a circle whose equation is $(x+1)^2+y^2=9$
   
   $(-1,-1)$
   $(-1,1)$
   $(-1,0)$
   $(1,0)$
6. A circle is centered at $(2,0)$ and passes through $(5,4)$. Find its equation.
   
   $(x+2)^2+y^2=25$
   $(x-2)^2+y^2=5$
   $(x+2)^2+y^2=5$
   $(x-2)^2+y^2=25$
7. A circle has center at $(1,-1)$ and its radius is $4$. What is its equation?
   
   $(x+1)^2+(y+1)^2=16$
   $(x-1)^2+(y+1)^2=16$
   $(x-1)^2+(y+1)^2=4$
   $(x-1)^2+(y-1)^2=16$
8. Which of the following points is not inside the circle $x^2+y^2=100$?
   $(8,5)$
   $(9,2)$
   $(3,9)$
   $(9,6)$
9. Which of the following points is on the circle $(x-1)^2+(y-2)^2=16$?
   $(6,1)$
   $(1,6)$
   $(-1,6)$
   $(-2,-3)$
10. Find the equation of a circle which passes through $(0,0),(6,0),(0,8)$.
    
    $x^2+y^2=5$
    $x^2+y^2=36$
    $(x+3)^2+(y+4)^2=25$
    $(x-3)^2+(y-4)^2=25$