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Prove 3(x+1)(x+7)-(2x+5)² is never positive

So,
3(x+1)(x+7)-(2x+5)(2x+5)
=3(x²+8x+7)-(4x²+20x+25)
=3x²+24x+21-4x²-20x-25
=-x²+4x-4

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Anonymous

  1. = -(x^2-4x+4)
    = -(x-2)^2

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    Steve

  2. The answer above didn't work

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    Anonymous

  4. Sorry It actually did

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    Anonymous

  5. I don't know what you mean by it "didn't work." It just shows that the expression is never positive.

    (x-2)^2 is a square, so it is always positive

    So, -(x-2)^2 is never positive.

    Trying to plug a formula into a request for a proof will never work. The logic is what counts.

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    Steve

  6. this was extremely useful. thank you

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    Anonymous

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