Math Problem Statement

Circle A in the xy-plane has the equation (x + 5)^2 + (y - 5)^2 = 4. Circle B has the same center as Circle A. The radius of circle B is two times the radius of circle A. The equation defining circle B in the xy-plane is (x + 5)^2 + (y - 5)^2 = k, where k is a constant. What is the value of k?

Solution

We are given two circles, Circle A and Circle B, in the xy-plane with their equations. Here's how we can break it down:

Circle A:

The equation for Circle A is: (x+5)2+(y5)2=4(x + 5)^2 + (y - 5)^2 = 4 This is the standard form of a circle equation (xh)2+(yk)2=r2(x - h)^2 + (y - k)^2 = r^2, where (h,k)(h, k) is the center and rr is the radius.

  • Center of Circle A: (5,5)(-5, 5)
  • Radius of Circle A: 4=2\sqrt{4} = 2

Circle B:

Circle B has the same center as Circle A but its radius is twice the radius of Circle A. Therefore, the radius of Circle B is: 2×2=42 \times 2 = 4 The equation for Circle B is given as: (x+5)2+(y5)2=k(x + 5)^2 + (y - 5)^2 = k Since the radius of Circle B is 4, and the equation of a circle is (xh)2+(yk)2=r2(x - h)^2 + (y - k)^2 = r^2, we can equate r2=kr^2 = k: k=42=16k = 4^2 = 16

Thus, the value of kk is 1616.


Do you have any questions or would you like more details? Here are some related questions for further practice:

  1. How would you write the equation of a circle with a center at (3,7)(3, -7) and a radius of 5?
  2. If Circle A had a radius of 3 instead of 2, what would be the value of kk for Circle B?
  3. What would the equation for Circle A be if its radius were halved?
  4. How do you find the equation of a circle given three points on its circumference?
  5. How does the equation of a circle change when it is translated horizontally by 2 units?

Tip: Remember that the general form of a circle's equation is directly tied to its center and radius. Always square the radius for the equation!

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Math Problem Analysis

Mathematical Concepts

Geometry
Circle Equations

Formulas

(x - h)^2 + (y - k)^2 = r^2 (Equation of a circle)
r^2 = k (Relating the radius to k)

Theorems

Pythagorean Theorem for Circle Equation

Suitable Grade Level

Grades 9-11