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Can someone help me factor this 5x^2+8x+9
What's the technique in factoring

  • Math -

    just a lot of experience, some guesses, and some luck. You know from looking at it that the factors will be of the form

    where the two a,b are one each of 1,9.

    You need 5b+9a = 8

    Now, even a cursory look assures you that there are no such a,b both positive where this can be the case.

    A quick check of the discriminant shows that it is 8^2-4*9*5 = 64-180 < 0, so there are no real roots. That means no factors over the rationals.

    Is there a typo here? The beast can certainly not be factored.

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