Question 308770
{{{y^2-7y+21x-3xy}}}


This is a factoring by grouping problem with a twist.  It might be helpful to rewrite this switching the last two terms.  You will see why when we do it.
{{{y^2-7y-3xy+21x}}}


Take out a factor of y from the first two terms, and a factor of -3x from the last two terms.
{{{y(y-7)-3x(y-7)}}}


Now, there is a common factor of (y-7):

{{{(y-7)(y-3x)}}}


Dr. Robert J. Rapalje, Retired
Seminole State College of Florida
Altamonte Springs Campus