Area of Triangles and Trapezoids

Area of a Triangle Formula to MEMORIZE!!!!

What do the letters stand for? A is area b is base of the triangle h is height of the triangle

Obtuse Triangle b h

Right Triangle h b

Acute Triangle b h b h

Question 1 What do you notice about the b and the h in the different triangles? * b and h will ALWAYS form a right angle*

Question 2 Is the height, h, a part of the triangle? -Only for right triangles. Otherwise, h is an imaginary line. * height, h, is also referred to as the altitude of a triangle.

Example 1 What is the area? Answer:

Example 2 Find the area. 9 cm 8 cm Answer:

Perimeter of Triangles To find the perimeter, ADD the 3 SIDES of the triangle. * Be careful, sometimes h is not one of the sides of the triangle.*

Example 1 Find the perimeter. 8 in 4 in 6 in 19 in Answer:

Area of a Trapezoid Formula to MEMORIZE!!!!

What is b 1 and b 2 ? b 1 and b 2 represent the parallel sides of a trapezoid. b 1 b 2 h b2 b2 b 1

Question 1 What do you notice about b 1 and b 2 and the h in the trapezoid? * they form a right angle*

Question 2 & 3 What happens if I put 2 trapezoids together? -They form a rectangle. What can you conclude about the area of 1 trapezoid versus a rectangle? - The area of a trapezoid would be HALF the area of a rectangle.

Question 4 Why do you ADD b 1 and b 2 in the formula? - Adding b 1 and b 2 represents the base of the rectangle. That’s why the formula is similar to the area of a rectangle formula.

Directions Find the perimeter and area of the following examples.

Example 1 6 m 12 m 8 m 9 m Perimeter: Area: 35 m

Example 2 Perimeter: Area: 26 m 4 m 9 m 6 m 7 m 5 m