What can be factored out of

Question

What can be factored out of y^2-4y

Answer 1

Each term in your expression has factors.  The term y^2 has factors y, y.  The term (-4y) has factors (-4), y.

 

Now, the expression may be factored because the terms share a factor (one of the y's).  Taking that common factor out, we get:

      y*(y-4)

 

Later, if you see this expression equal to 0, as in   y*(y-4) = 0,  you will realize that this can happen only if y=0  or y=4  or both.