Algebra tiles can be used to visualize
how a perfect square trinomial can be formed.
The tiles could be used by students or simply used by the teacher as a
warmup to this concept.
Example 1:
What is needed to create a perfect square trinomial for:

Use the algebra tiles to create
a square. What tiles
will be needed to complete the square?
After viewing several examples,
help students to see the pattern for finding the needed constant
term. "Take half of the coefficient of the xterm
and square it." 
Example 2:
What is needed to create a perfect square trinomial for:

Use the algebra tiles to create
a square. Red tiles
represent negative values. What tiles will be needed to
complete the square? What will be the sign of these needed
tiles?
This example should solidify
the concept that the needed constant term will be a positive
value. 
