Well if the expressions and are factors of the given polynomial, and must be its roots.

So just substitute and then and see if the equation

is satisfied.

so for , the value of the polynomial is,

Hence the above equation is satisfied. So x-1 is a factor.

Now, insert and prove that the value of the polynomial becomes zero.

so as x=1 and x=2 are the roots of the given polynomial is a factor.