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Leaving Certificate - Algebra

  • 12-11-2008 11:24pm
    #1
    Megatron_X
    Registered Users, Registered Users 2 Posts: 117 ✭✭


    Algebra in question:
    Sum and Product of the Roots of a Quadratic Equation

    Hey, I got a couple of maths questions to finish for today, and I can do all of them but 1, which is at the end of the chapter so I think it's a sample of one of the easier LC ones.

    Here's what it says:

    Find the value of k that will leave 4 in the difference between the roots of the equation x^2+2kx+k+2=0.

    It's really bugging me, and I'd appreciate an answer!


Comments

  • #2
    Cokehead Mother
    Closed Accounts Posts: 773 ✭✭✭Cokehead Mother


    I would write the two roots in terms of k using the quadratic formula to begin with. Then use the fact that the bigger root minus the smaller root is 4.


  • #3
    MathsManiac
    Registered Users, Registered Users 2 Posts: 1,595 ✭✭✭MathsManiac


    Alternatively, you could note that (alpha - beta)^2 would then equal 16, and this can be written as (alpha + beta)^2 - 4 alpha.beta, etc.

    (This leaves you with the same equation in k as you get via Cokehead's suggestion.)


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