Factor 5x^2+28x -12 (show the steps )

I'd start by finding the roots of the given expression.  From these roots you can write the factors.
        -28 plus or minus sqrt(28^2 - 4(5)(-12)
x  =
                                      10
           -28 plus or minus sqrt(784+240)
    =
                              10
         -28 plus or minus 35 (approx)
    =
                         10
          35-28                -28-35
     = and    These roots are only approximate.  However,
              10                     10        if we treat them as exact, with one root
                                                   equal to 7/10 and the other -63 / 10     
                                                                                               
then the factors of the polynomial would be, approx., x-7/10  and x+63/10.

Please double check to ensure that you've copied down the problem completely and accurately.  Thanks.