The answer is: " 2y (x³ − 9x² − 45) " .
___________________________________
Given: 2x³y − 18x²y − 90y ;
___________________________________
We can factor out a "2y" ; by looking out the "90y" as the term with the least number of variables. We see that the terms has one "y" only; and that ALL the all terms in the this expression have ONE "y" ; so we can factor out a "y".
Then, we see that "2" is the smallest term (coefficient, in this case), in the expression, that that in the term: "90y" ; "90" is divisible by "2" ; as are all the other coefficient(s) in the expression (in this case, the one remaining, which is "18". So, we can factor out a "2y" ; as follows:
___________________________________________
→ 2y (x³ − 9x² − 45) ;
___________________________________________
Neither this expression — nor the expression in parentheses — can be factored any further; so, this is our answer.
___________________________________________
