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Math Help - Quadratics

  1. #1
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    Quadratics

    I need to put y=(x+3)(x+4) into quadratic form and find the values of x.

    I solved the quadratic equation as y= x +7x+12
    And by using the quadratic formula I got the answer of x=-3 and -4 but when I substitute those values into the equation, I get different answers.

    I thought you were meant to get two values for x but they would both equal the same number when put into the equation.

    Am I doing something wrong here or can someone explain what's going on?
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  2. #2
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    Quote Originally Posted by J4553 View Post
    I need to put y=(x+3)(x+4) into quadratic form and find the values of x.

    I solved the quadratic equation as y= x +7x+12
    And by using the quadratic formula I got the answer of x=-3 and -4 but when I substitute those values into the equation, I get different answers.

    I thought you were meant to get two values for x but they would both equal the same number when put into the equation.

    Am I doing something wrong here or can someone explain what's going on?
    You do realise that if 0 = (x+3)(x+4) then either x + 3 = 0 => x = -3 or x + 4 = 0 => x = -4 .....

    So your solutions are correct. It would seem that you are doing the arithmetic incorrectly after substituting the values into the equation.
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  3. #3
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    It was my calculator: when I put in -3 it gives me the answer of -9
    I didn't realise I had to enter it as (-3) to get the answer of 9
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  4. #4
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    Thumbs up Angel (Best Solution)

    your answers are correct but why do you want to put it again?

    if you want to check your answer whether these are correct or not then put both values of x one by one and check y is becoming 0 for each value of x, if yes then your answers are correct if not then your answers are not correct..............................






    In this equation, no y-intersept. this eqaution is not touching the y-axis.
    Last edited by Angel; November 2nd 2008 at 12:08 AM.
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  5. #5
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    Also,
    When I'm graphing the quadratic, does it mean that the line goes through the points -3 and -4 on the x-axis?

    How far down the y-axis should the parabola go and what is the y intercept??
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  6. #6
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    Quote Originally Posted by J4553 View Post
    Also,
    When I'm graphing the quadratic, does it mean that the line goes through the points -3 and -4 on the x-axis? Mr F says: Yes, it does mean that the parabola goes through the points x = -3 and x = -4 on the x-axis.

    How far down the y-axis should the parabola go Mr F says: Find the coordinates of the turning point.

    and what is the y intercept?? Mr F says: Substitute x = 0 and solve for y.
    ..
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  7. #7
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    Thanks Mr. Fantastic
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  8. #8
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    Quote Originally Posted by Angel View Post
    [snip]
    In this equation, no y-intersept. this eqaution is not touching the y-axis.
    *Ahem* Yes there is. It does.
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  9. #9
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    Quote Originally Posted by Angel View Post
    your answers are correct but why do you want to put it again?

    if you want to check your answer whether these are correct or not then put both values of x one by one and check y is becoming 0 for each value of x, if yes then your answers are correct if not then your answers are not correct..............................






    In this equation, no y-intersept. this eqaution is not touching the y-axis.
    Please quote what you are replying to so we can all have some idea what you are refering to.

    Also do not use a large font size for routine answers, you look like you are just attention seeking.

    (treat these comments and any others made by admins/mods and helpers as warnings)

    CB
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