You should know the following formulae to work out the areas of these shapes:

**Rectangle**

You must know:

- the
**base**length - the perpendicular
**height**from the base to the top.

Area of **rectangle** = base × height

**Parallelogram**

You must know:

- the
**base**length - the perpendicular
**height**from the base to the top.*(NOT the slant height)*

Area of **parallelogram** = base × height

**Triangle**

You must know:

- the
**base**length - the perpendicular
**height**from the base to the apex.*(NOT the slant heights)*

Area of **triangle** = ½ base × height

or

Area of **triangle** = base × height ÷ 2

**Example 1**

Can an area formula be used to work out the area of this parallelogram, and if so, which one?

**Answer**

This is a parallelogram.

We must know:

- the
**base**length - the perpendicular
**height**from the base to the top.*(NOT the slant height)*

We know the **base **length** **and** **the** slant height**, but **not **the **perpendicular height**.

**No**, we cannot use the area formula.

**Example 2**

Can an area formula be used to work out the area of this triangle, and if so, which one?

**Answer**

This is a triangle.

We must know:

- the
**base**length - the perpendicular
**height**from the base to the top.*(NOT the slant height)*

If we turn our heads to the left, the **base length is 12 cm **and the **perpendicular height is** **6 cm**.

*We do not need to know the slant height of 10 cm to use the formula.*

**Yes**, we can use the area formula:

**Area of triangle = ½ base × height**