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Equation of a circle

  • 12-06-2010 3:47pm
    #1
    Dubs
    Registered Users Posts: 365 ✭✭


    A question that has been bugging me all year. In higher level, when your asked to give the equation of a circle do you use the formula
    (x-h)^2 + (y-k)^2 = r^2

    Or

    x^2 + y^2 + 2gx + 2fy +c ?

    Iv looked up the marking schemes for some questions and it varies which ones they use in the answers. Can you use either?

    Also, any predicitions on what proofs will come up? :D


Comments

  • #2
    EuropeanSon
    Registered Users Posts: 2,819 ✭✭✭EuropeanSon


    Both are correct. As for the theorums, I'd say the trig ones, like cos(A-B), sine rule, cosine rule etc.
    The reason Marking Schemes vary is that sometimes you get one first, ie. If you find it in one form, they stop, and don't convert it to the other.


  • #3
    ajjmk
    Registered Users Posts: 338 ✭✭ajjmk


    i was told to use (x-h)^2 + (y-k)^2 = r^2 if you're looking for the equation & can find the radius & centre.. :)


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