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#33609

scale

circles

geometry

hard

90 sec

Circle A in the $x y$ -plane has its center at the origin and an area of $16 π$ . Circle B has the same center as circle A. The area of circle B is 9 times the area of circle A. The equation defining circle B in the $x y$ -plane is $x^{2} + y^{2} = k$ , where $k$ is a constant. What is the value of $k$ ?

• Up to 5 characters (6 if negative). Only numbers, decimal (.), fraction (/), negative (-).
• Fractions must be in lowest terms.
• Mixed numbers must be converted to improper fractions.