Not every shape is a rectangle. An L-shape is made of two rectangles stuck together, so you can cut it into rectangles, find each area and add.
Why it works
Area adds up: if a shape is made of two pieces that do not overlap, its area is the area of one piece plus the area of the other. A cut along a side of the corner turns the L into two rectangles, and you know how to find the area of a rectangle.
Key idea
To find the area of an L-shape: cut it into two rectangles, find the side lengths of each, multiply, and add.
Worked example: Cut and add
Find the area of the L-shape in the picture.
- Blue rectangle: 5 wide and 6 tall: $5 \times 6 = 30$.
- Gold rectangle: 3 wide and 4 tall: $3 \times 4 = 12$.
- Add: $30 + 12 = 42$ square meters.
Answer: 42 square meters
Worked example: Another way: take away
Find the same area by thinking of the whole 8-by-6 rectangle with a corner missing.
- Whole rectangle: $8 \times 6 = 48$.
- Missing corner: 3 wide and 2 tall: $3 \times 2 = 6$.
- $48 - 6 = 42$. Same answer.
Answer: 42 square meters
Common mistake
Multiplying the two longest sides. $8 \times 6 = 48$ is the area of a full rectangle, but this shape has a corner cut out. Check: does the shape fill the whole 8-by-6 box? It does not, so its area must be less than 48.