do you guys knew this formula this make very easy than this video if I have 3x^2-2x-8 right so a x b, a +b, if I multiply 3 x -8 =-24  factors of ---24 is 4  6  right so 4x6 24 and -6+4 =-24 we 

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I've come back to this problem to try what I believe is your method.  (3)(-8) = -24 found by multiplying the first and last coefficients of the original polynomial.From all of the possible factors of -24 I want a pair that adds to -2.  That givs us  only -6 and 4.Now replace the middle term of the polynomial with (-6x) and 4x3x^2 -6x + 4x -8..   Group these terms to have a common binomial.3x(x-2) + 4(x-2).     Factor out the common binomial(3x + 4)(x-2)  and you are done!  Okay that is nice!