In this case you can factorize the expresion using common factor twise as follows:
first factor [tex]a[/tex] in the two first terms and use the asociative law to associate the third and fourth terms:
[tex]a(x-1) + (x-1)[/tex]
In the last expression, we have once again a common factor, namely [tex](x-1)[/tex]. So we factorize by common factor to obtain:
[tex](x-1)(a+1)[/tex]
and this complete the answer.
