area of triangles and trapezoids. area of a triangle formula to memorize!!!!
TRANSCRIPT
Area of Triangles
andTrapezoids
Area of a Triangle
Formula to MEMORIZE!!!!
hbA 2
1
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
hb 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?
16
12
96)1216(21 Answer:
Example 2
• Find the area.
9 cm
8 cm
Answer: 236)89(21
cm
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 in6 in
19 in
Answer: in331986
Area of a Trapezoid
Formula to MEMORIZE!!!!
)(21
21 bbhA
What is b1 and b2?
• b1 and b2 represent the parallel sides of a trapezoid.
b1
b2
h
b2
b1
Question 1
• What do you notice about b1 and b2 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 b1 and b2 in the formula?
- Adding b1 and b2 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 m9 m
Perimeter:
Area:
35 m272m
Example 2
Perimeter:
Area:
26 m25.32 m
4 m
9 m
6 m 7 m
5 m