Solution - Simplification or other simple results

Step  1  :

Trying to factor by splitting the middle term

 1.1     Factoring  y²-8y+15 

The first term is,  y²  its coefficient is  1 .
The middle term is,  -8y  its coefficient is  -8 .
The last term, "the constant", is  +15 

Step-1 : Multiply the coefficient of the first term by the constant   1 • 15 = 15 

Step-2 : Find two factors of  15  whose sum equals the coefficient of the middle term, which is   -8 .

Step-3 : Rewrite the polynomial splitting the middle term using the two factors found in step 2 above,  -5  and  -3 
                     y² - 5y - 3y - 15

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

Final result :

  (y - 3) • (y - 5)