Prove It!

We are working on concepts of AREA and perimeter in math.  

One problem asked:

• Sharon knows the perimeter of a quadrilateral. She knows three side lengths of the quadrilateral.  She says she can find the unknown side length by subtracting.  Is she right?  Justify your answer using words, drawing, pictures, or numbers.  

Here are some of the students discussing and "justifying" their answers.  

They could be heard saying things like... 

"Do you see WHY that works?" 

"We have to show HOW we know."

"Quadrilaterals don't have to have four equal sides."