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Math Help - Quadratic equation by factorisation (without using the standard formula)?

  1. #1
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    Quadratic equation by factorisation (without using the standard formula)?

    X2 -4x -165 = 0


    must show that you have checked your answer by substituting the values obtained into the original expression

    show each step of the solution,

    Thanks
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  2. #2
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    Thumbs up

    The equation can be factorized by inspection. The two numbers in the brackets must multiply together to make -165, so.....

    If you find all the prime factors of 165, they are 3, 5, and 11. and note that 3x5 = 15

    You also know that the sum of the two numbers in the brackets must be -4.

    and.....
    11x-15=-165
    11+(-15)=-4

    x^2-4x-165 = (x+11)(x-15)
    Last edited by watto23; March 31st 2010 at 02:46 AM. Reason: better understanding
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  3. #3
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    this may sound like a silly question but am new on here, what does this symbol represent (^), thanks for your help mate. is your answer to my question the fully solved answer??
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  4. #4
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    Thumbs up

    yer mate thats the answer. The ^ means 'to the power of'

    so x^2 is x squared
    and x^3 is x cubed etc.
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  5. #5
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    Cheers mate
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  6. #6
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    one more question mate, bit cheeky of me i know sorry.
    Solve the following quadratic equation by implementing the formula method.
    Answer to 3 significant figures

    Can you Show each step to the solution please.
    5x2 + 5x 4x2 + 2x= 20

    The standard form of the quadratic equation is
    Ax2 + bx + c = 0

    How would this be solved??
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  7. #7
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    5x2 + 5x 4x2 + 2x= 20
    take x terms together n x^2 trems together
    so u get

    x^2+7x-20=0
    u cannot factorise thie equation
    if d equation is ax^2+bx+c=0
    so use (-b+sq(b^2-4ac))/2a n (-b-sq(b^2-4ac))/2a
    these two r the values of x
    i guess u know this
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