This shape is made from two identical squares overlapping. Expressions A2.2 Extension Starter This shape is made from two identical squares overlapping. (a) Find an expression for the perimeter of the shape. Both squares have sides 10 cm long. (b) Find an expression for the perimeter of the shape using b. (c) Find an expression for the perimeter of the shape using a. Preamble An activity involving some relatively difficult algebraic manipulation. Some support may well be needed, particularly in parts (b) and (c). Possible content Algebraic simplification, revision of perimeter. Resources None. Solutions/Notes Perimeter is 6a + 8b (opportunity to stress importance of simplification). Perimeter is 6(a + b) + 2b = 60 + 2b (since a + b = 10). b = 10 − a so the perimeter can be written as 60 + 2(10 − a) = 80 – 2a