Solution - Simplification or other simple results

Step  1  :

Equation at the end of step  1  :

  ((3•7x2) -  25x) -  4

Step  2  :

Trying to factor by splitting the middle term

 2.1     Factoring  21x²-25x-4 

The first term is,  21x²  its coefficient is  21 .
The middle term is,  -25x  its coefficient is  -25 .
The last term, "the constant", is  -4 

Step-1 : Multiply the coefficient of the first term by the constant   21 • -4 = -84 

Step-2 : Find two factors of  -84  whose sum equals the coefficient of the middle term, which is   -25 .

Step-3 : Rewrite the polynomial splitting the middle term using the two factors found in step 2 above,  -28  and  3 
                     21x² - 28x + 3x - 4

Step-4 : Add up the first 2 terms, pulling out like factors :
                    7x • (3x-4)
              Add up the last 2 terms, pulling out common factors :
                     1 • (3x-4)
Step-5 : Add up the four terms of step 4 :
                    (7x+1)  •  (3x-4)
             Which is the desired factorization

Final result :

  (3x - 4) • (7x + 1)