Question 862451
Tell her to try doing this:


Perform the multiplication, (x-a)(x+b).  Simplify and put into the form of decreasing powers of x.  Notice that this will be a trinomial with leading term of x^2.


Perform the multiplication, (x+a)(x+b).  Simplify, and do as before...  Compare the two different products.


Perform the multiplication, (x+a)(x+a).  Simplify, and as before, arrange into decreasing powers of x.


LASTLY, perform the multiplication, (x+a)(x-a).  Simplify this.  She now has a formula for the difference of two squares.  YES, YES, YES.  This will help to solve for x in x^2-4=0, because now the quadratic expression can be factored.  One or the other factors must be zero.   Not both at the same time.  Only one of them at a time.


Note carefully, x^2-4=0 has no "y".  It only has variable x.