Half the Rectangle

Part of the Triangles section of Coddy's Geometry journey. Lesson 22 of 71.

Draw a rectangle around a triangle so that they share the base and the rectangle reaches the top of the triangle. The triangle takes up half of the rectangle. A rectangle with base 10 and height 4 has area 40, so the triangle inside it has area 20. The area of a triangle is half the base times the height.

$A triangle with base 10 and height 4 drawn inside the rectangle it is half of$

The triangle is half of a 10 by 4 rectangle

A = 1/2 × b × h

A = 1/2 × 10 × 4 = 20

Area is measured in square units, because it counts the unit squares inside the shape. If the sides are in centimetres, the area is in square centimetres. The base is one side of the triangle. The height is the straight distance from that base up to the opposite vertex, and it meets the base at a right angle. The next lesson shows which line counts as the height.