Solution - Simplification or other simple results

Step  1  :

Trying to factor by splitting the middle term

 1.1     Factoring  -x²+16x+36 

The first term is,  -x²  its coefficient is  -1 .
The middle term is,  +16x  its coefficient is  16 .
The last term, "the constant", is  +36 

Step-1 : Multiply the coefficient of the first term by the constant   -1 • 36 = -36 

Step-2 : Find two factors of  -36  whose sum equals the coefficient of the middle term, which is   16 .

Step-3 : Rewrite the polynomial splitting the middle term using the two factors found in step 2 above,  -2  and  18 
                     -x² - 2x + 18x + 36

Step-4 : Add up the first 2 terms, pulling out like factors :
                    -x • (x+2)
              Add up the last 2 terms, pulling out common factors :
                    18 • (x+2)
Step-5 : Add up the four terms of step 4 :
                    (-x+18)  •  (x+2)
             Which is the desired factorization

Final result :

  (x + 2) • (18 - x)