Finding the Center and Radius of a Sphere: A Homework Question

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SUMMARY

The equation of the sphere given is 16x² + 16y² + 16z² - 96x + 32y = 5. By completing the square, the center of the sphere is determined to be (3, -1, 0). The radius calculation initially attempted was incorrect; the correct method involves ensuring that all terms added to the left side are multiplied by 16, leading to a radius of √15 / 4. This highlights the importance of maintaining balance in equations when manipulating algebraic expressions.

PREREQUISITES
  • Understanding of completing the square in algebra
  • Familiarity with the standard equation of a sphere
  • Basic knowledge of algebraic manipulation
  • Ability to solve quadratic equations
NEXT STEPS
  • Review the standard form of a sphere's equation
  • Practice completing the square with different equations
  • Learn about the geometric interpretation of spheres in three-dimensional space
  • Explore methods for solving algebraic equations involving multiple variables
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Students studying algebra, particularly those tackling geometry and three-dimensional shapes, as well as educators looking for examples of completing the square in practical applications.

bobbarkernar
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Homework Statement



The equation represents a sphere.

16x^2+16y^2+16z^2-96x+32y=5

Find its center, and radius



Homework Equations





The Attempt at a Solution


i found the center by completing the square:

16[(x^2-6x+9)+(y^2+2y+1)+(z^2)]=5+9+1
16[(x-3)^2 +(y+1)^2 +(z+0)^2]=15

the center is (3,-1,0)
i thought the radius would be (15^.5)/4 but that was incorrect if someone could please help me thank you
 
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bobbarkernar said:

Homework Statement



16[(x^2-6x+9)+(y^2+2y+1)+(z^2)]=5+9+1
16[(x-3)^2 +(y+1)^2 +(z+0)^2]=15

You forgot to multiply the added 1 and 9 on the right side by 16. Either multiply everything out on the left side and see what needs to be added to equalize the right side or try going back and dividing everything by 16 before completing the square.
 
Last edited by a moderator:
ok i see what i did wrong. thank you very much
 

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