This document provides formulas and examples for calculating the areas of rectangles, parallelograms, and triangles. It explains that the area of a rectangle is length times width, the area of a parallelogram is base times height, and the area of a triangle is one-half base times height. The document includes practice problems that require applying these formulas to find missing values like areas, perimeters, and heights.

1. 11.1 Area of Parallelograms & Triangles February 29, 2012
11.1 Areas of Triangles & Parallelograms
Objectives:
1. To develop the concept of area.
2. Apply area formulas to solve problems.
What is area?
Rules for Using Formulas:
1. Always state the formula you are using first!
2. Identify the knowns & unknowns for each variable in the formula.
3. Plug the knowns into the equation.
4. Solve for the unknown using algebra.
5. Be sure to include a label with your answer.
Formula for:
Area of a Rectangle: A = bh
The base and height are
always perpendicular to
each other.
Find the area of the rectangle:
A = _____
22m 10.5m
HW pg. 723 #4­26 evens 1

2. 11.1 Area of Parallelograms & Triangles February 29, 2012
Area of a Parallelogram: A = bh
The altitude will be
perpendicular to the base.
Find the area of the parallelogram:
A = _____
12m
6m
20m
HW pg. 723 #4­26 evens 2

3. 11.1 Area of Parallelograms & Triangles February 29, 2012
Area of a Triangle = 1/2bh
Base & height are always
h
perpendicular to each other!
b
Triangles can have multiple appearances:
Find perimeter and area of the triangle.
17
10
8
P = 48 units
A = 84 units2
21
HW pg. 723 #4­26 evens 3

4. 11.1 Area of Parallelograms & Triangles February 29, 2012
Find the height of the parallelogram. Area = 100 m2
20 m
x
Find the area of the rectangle.
18 m Perimeter = 50 m
y
HW pg. 723 #4­26 evens 4

5. 11.1 Area of Parallelograms & Triangles February 29, 2012
Find the area and perimeter of the shaded region.
18m 6cm 1cm
15m 9m 8cm 3cm
5cm
10m 11cm
P = 66 m
P = 38 cm
A = 222 m2 A = 77 cm2
HW pg. 723 #4­26 evens 5

6. 11.1 Area of Parallelograms & Triangles February 29, 2012
HW:
11.1 pg. 723
#4-26 evens
HW pg. 723 #4­26 evens 6