x2 - 20 x + 100
In this case we've got three terms & it's a quadratic polynomial. Notice down as well that the constant is perfect square & its square root is equal to 10. Notice as well that 2(10) =20 & it is the coefficient of the x term. Thus, it looks like we've got the second special form above. The accurate factoring of this polynomial is following,
x2 - 20 x + 100 =(x -10)2
To be honest, it may have been simpler to just employ the general procedure for factoring quadratic polynomials in this case instead of checking that it was one of the special forms, but we did have to see one of them worked.