Perimeter Flashcards

All 6 cards in this deck

What is the perimeter of a 2D shape?

The total distance around the outside of the shape.

What is the formula for the perimeter of a rectangle?

e.g. a rectangle 5 cm by 3 cm

$P = 2(l + w)$

e.g. $2(5+3) = 16$ cm

On a rectilinear (L-shaped) shape, how do you find a missing horizontal side length?

The horizontal parts on one side add up to the full width on the other side. If the missing side is part of the width, subtract; if it is the full width, add.

e.g. full width $10$ cm, one part $4$ cm: $10 - 4 = 6$ cm

True or false? When a composite shape is split into rectangles, the lines drawn inside it count towards the perimeter.

False. Only the outside edges of the shape are added to give the perimeter.

What units is a perimeter measured in?

Units of length, e.g. mm, cm, m — never squared units.

What are the steps to find the side lengths of a rectangle from its perimeter when the sides are algebraic?

e.g. sides $x+1$ and $2x$ cm, perimeter 20 cm

1. Write the perimeter as an expression: $2(x+1+2x) = 20$
2. Solve the equation: $6x + 2 = 20$, so $x = 3$
3. Substitute back: sides are 4 cm and 6 cm