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Math Help - Find k

  1. #1
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    Find k

    Find a number k such that 4 and 1 are the solutions
    of x^2 - 5x + k = 0.

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  2. #2
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    Quote Originally Posted by sologuitar View Post
    Find a number k such that 4 and 1 are the solutions
    of x^2 - 5x + k = 0.
    sub in 4 or 1 for x and solve for k
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  3. #3
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    WOW!

    Quote Originally Posted by skeeter View Post
    sub in 4 or 1 for x and solve for k
    I can't believe the problem is that easy.
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  4. #4
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    It sure is! And I will confess that I would have suggested either

    1) Use the quadratic formula: x= \frac{5\pm\sqrt{25- 4k}}{2}
    and set \frac{5+ \sqrt{25- 4k}}{2}= 4 and \frac{5- \sqrt{25- 4k}}{2}= 1 and solve for k
    or

    2) Write x^2- 5x+ k= (x- 1)(x- 4), multiply it out and solve for k.

    But skeeter's suggestion is far simpler than either of those.
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  5. #5
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    Thanks...

    Quote Originally Posted by HallsofIvy View Post
    It sure is! And I will confess that I would have suggested either

    1) Use the quadratic formula: x= \frac{5\pm\sqrt{25- 4k}}{2}
    and set \frac{5+ \sqrt{25- 4k}}{2}= 4 and \frac{5- \sqrt{25- 4k}}{2}= 1 and solve for k
    or

    2) Write x^2- 5x+ k= (x- 1)(x- 4), multiply it out and solve for k.

    But skeeter's suggestion is far simpler than either of those.
    Thank you for the different methods.
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  6. #6
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    The really nice thing is that all three methods give the same answer!
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