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    ferceballos1's Avatar
    ferceballos1 Posts: 7, Reputation: 1
    New Member
    		  
    #1

    Jun 27, 2007, 09:54 AM
    algebra ll
    I need help with roots...




    the problem is...

    find the value of "k", given that one solution of the equation
    x^2-kx+21=0 is 3.


    please I really need it..
    nicespringgirl's Avatar
    nicespringgirl Posts: 1,237, Reputation: 187
    Ultra Member
    		  
    #2

    Jun 27, 2007, 10:03 AM
    k=-10
    hey, but I hope yo uhave done some work before you ask hw question sweetie!
    ferceballos1's Avatar
    ferceballos1 Posts: 7, Reputation: 1
    New Member
    		  
    #3

    Jun 27, 2007, 10:06 AM
    Of course I try my best...


    I am just looking for a little help...

    Sometimes some problems are just so hard that is easy to give up...
    But thanks... but after you know the answer they look so easy... thanks
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
    Expert
    		  
    #4

    Jun 27, 2007, 10:08 AM
    Since the equation is a quatratic, you need to think about how it could be factored to yields one solution of 3. Recall that all quadratic equations have two solutions, let's call them A and B, and can be written as:

    (x-A)(x-B) = 0.

    In this case you are told that one of the answers is 3. You can replace the A with 3, and you have:

    (x-3)(x-B) = 0.

    Multiply this out, compare to the formula you were given , and you should be able to solve for B, and then k. Try it and let us know how it goes.
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