MATHEMATICS Perimeter

Lesson Objectives The aim of this powerpoint is to help you… to find missing side lengths to find perimeters of shapes

What is ‘Perimeter’? Perimeter is the distance all the way around the outside of a shape. You ADD all the individual distances of every side (around the outside) together. However, you may need to work out missing sides first!

What is the perimeter measured in? Perimeter is a distance (or length). Its metric units are millimetres (mm), centimetres (cm), metres (m) or kilometres (km). Its imperials units are inches (in), feet (ft), yards (yd) or miles.

Missing Sides To find missing sides… Look for symbols to show whether sides have the same length (a small line going through two or more sides/lines) Compare the missing side with the lengths of other parallel sides and work out the difference or sum (as appropriate).

Example 1 This is a triangle Although I have only been given one side, the little lines through each side show they are all of equal length All three sides are 8m P = 8m + 8m + 8m = 24m 8m

Example 2 Here is an L-shape Before we calculate its perimeter, we need to work out the length of the red side. 2mm 5mm 8mm4mm 6mm

Example 2 (cont’d) Here are the isolated vertical sides of the L- shape The red side is vertical and is found by taking the green side away from the yellow side Now we have all side lengths 5mm 8mm ( 8mm – 5mm =) 3mm

Example 2 (cont’d) Start at the top left and move in a clockwise direction: Perimeter = 2mm + 5mm + 4mm + 3mm + 6mm + 8mm = 28mm 2mm 5mm 8mm4mm 3mm 6mm

Quick Practice Find the perimeter of each of these shapes. 3mm 7mm 6mm 11mm 2m 7cm 3m 9m 2m 12cm 8m 7mm

Quick Practice - Solutions 7cm 12cm 7cm 12cm This side is the same as the 12cm on the bottom This side is the same as the 7cm on the right 7cm 12cm So the perimeter is: = 38cm

Quick Practice - Solutions 3mm 7mm 6mm 11mm This side is the same as the 11mm on the right hand side This side goes all the way across from left to right so is the same as the 3mm + 6mm + 7mm = 16mm 7mm This side is the same as the 7mm on the right hand side of the dip 7mm 11mm 16mm So the perimeter is: = 68mm

Quick Practice - Solutions 2m 9m 2m 8m 3m 2m 9m 2m 8m 3m Top to bottom (using right hand side) = = 11 Top to bottom on left hand side must also equal 11, so this side must be 9 (+ 2 = 11) 9m So the perimeter is: = 44m Left to right (using bottom sides) = = 11 Left to right using top sides must also equal 11, so this side must be 9 (+ 2 = 11)

What next? Print out the notes called PAV1-Perimeter. Read through them and make sure you answer any questions. Work through the MyMaths lesson and then its online homework called Perimeter found at: Save and complete the worksheet: Perimeter-S1.xlsx Now move on to the PAV2a powerpoint