Quantcast

A community for students. Sign up today!

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

stupidinmath

  • 10 months ago

If the center of the circle x^2 + y^2 + ax + by + 2 = 0 is point (4,-8), what is a + b? a. -8 b. -4 c. 4 d. 8 e. 24

  • This Question is Closed
  1. MrNood
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    It is rare in life to find someone who would call themselves 'stupid in English' or 'stupid in sport' Maths is only another skill to be learned and enjoyed like any other learning. It is not a badge of pride to 'not be able to do maths'

  2. stupidinmath
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    i know..

  3. surjithayer
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 1

    complete the squares and equate the centre.

  4. mathmale
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    I'd go so far as to try opening a new account with OpenStudy, so that you don't go on labeling yourself with such a derogatory term. It's not funny and does you no good.

  5. mathmale
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Hint: the equation of a circle with radius r and centered at (h,k) is\[(x-h)^{2}+(y-k)^{2}=r ^{2}\]. Hope this puts you on track towards finding a solution to this problem.

  6. mathmale
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Please demo how you'd complete the square: x^2 + 6x

  7. RadEn
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    just an alternative : if given the equation of circle x^2 + y^2 + ax + by + c = 0, then the centre is (-a/2 , -b/2). knowed the centre is (4, - 8) so, -a/2 = 4 solve for a also -b/2 = -8 solve for b after that, you can determine the value of a + b

  8. stupidinmath
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    i think its a..?

  9. stupidinmath
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    -8

  10. RadEn
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    have you solve them : -a/2 = 4 a = ... -b/2 = -8 b = ...

  11. surjithayer
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 1

    \[\left( x^2+ax+\left( \frac{ a }{2 } \right)^2 \right)+\left( y^2+by+\left( \frac{ b }{ 2 } \right)^2 \right)=-2+\left( \frac{ a }{ 2 } \right)^2+\left( \frac{ b }{2 } \right)^2\] \[\left( x-\frac{ a }{2 } \right)^2+\left( y-\frac{ b }{ 2 } \right)^2=-2+\frac{ a^2 }{4 }+\frac{ b^2 }{4 }\] centre is \[\left( \frac{ -a }{ 2 } ,\frac{ -b }{2 }\right)\] \[\frac{ -a }{ 2 }=4,a=-8,\frac{ -b }{2 }=-8,b=-8*-2=16\]

  12. stupidinmath
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    -16 - 8.

  13. stupidinmath
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    oh... positive 8?

  14. mathmale
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Dear Math Whiz: Why not try doing some of these calculations yourself and then sharing the results? Those trying to help you could then give you more specific and useful feedback.

  15. surjithayer
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 1

    we can also find by comparing with \[x^2+y^2+2gx+2fy+c=0,where~centre~is~\left( -g,-f \right) ~and radius=\sqrt{g^2+f^2-c}\]

  16. surjithayer
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 1

    radius=\[\sqrt{g^2+f^2-c}\]

  17. mathmale
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    I still think completing the square is a more readily understandable approach. But first, Math Whiz (I refuse to call you stupidinmath), are you familiar with completing the square?

  18. MrNood
    • 10 months ago
    Best Response
    You've already chosen the best response.
    Medals 0

    Welcome to Math Whiz

  19. Not the answer you are looking for?
    Search for more explanations.

    • Attachments:

Ask your own question

Ask a Question
Find more explanations on OpenStudy

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.