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May 2013

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This is where you'll find the latest happenings, news, & ideas in math teaching

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My videos at YouTube show you how to teach concepts.
How to help students with multiplication tables?

The ideas in this geometry lesson are taken from Math Mammoth Geometry 1 book.

Area of rectangles
Free geometry lesson plan from HomeschoolMath.net

The video below shows some varied exercises about the area of rectangles.

When we think of the area of something, we think how much ground it is covering (or would cover). For example, the football field covers a certain amount of ground. The stamp covers a tiny amount of ground if placed on ground. A sheet of paper covers more than a stamp but less than a football field.
Area is always measured in squares of some size. People often use square inches, square feet, square miles, square centimeters, and square meters for measuring area. We use the superscript “2” with a unit of length to indicate the “squaring”. For example, 8 in2 means 8 square inches, and 120 cm2 means 120 square centimeters.
The area of this square is 1 square centimeter, or 1 2.	The area of this square is 1 square inch or 1 in2.
Each tiny square has an area of 1 square millimeter, or 1 mm2. The area of the whole square is 100 mm2.
The total area of this rectangle is 6 cm2, or 6 square centimeters.	If no particular unit of length is given for the sides of a rectangle, we just use the word “unit”. The sides are 7 and 4 units, and the area is 28 square units.

1. Find the areas of these rectangles. No particular unit is given,
   so we use “square units”.

a. ________ square units     b. ________ square units     c. ________ square units

d. ________ square units      e. ________ square units

The following pictures are not to scale. They illustrate some other units of area. You can use multiplication to find how many square inches this rectangle covers: 2 in × 4 in = 8 in2. The area of this square is 1 square foot or 1 ft2. The area of this square is 1 square mile, or 1 mi2     Here again multiplication does the trick: Area = 8 km × 4 km = 32 km2. If the figure is some other shape than a rectangle, we still use little squares to measure its area. It is just more difficult to find out how many little squares it covers, and we may have to use partial (fractional) squares as well.

You can find the area of a rectangle by multiplying the side lengths.

2.  Draw a square with the area of...

3. Find the areas of the rectangles when the sides are known. Remember to use
   the right unit for area.

4. Find the missing measurements.

a.

b. [available in the book]

c. [available in the book]

5. Draw a figure.

a.  A rectangle with area 20 square units

b. A square with area 16 square units

c.  An L-shape with area 18 square units

6. How many square units is in the area of these shaded shapes?

7. Draw three different rectangles that have the area of 30 square units.

8. The side of each little square is 3 cm.      What is the area of the shaded rectangle?      Don't get fooled!

9. Challenge. Find the areas of the shaded figures. Hint: In (c), divide the figure into two rectangles.

The ideas in this geometry lesson are taken from Math Mammoth Geometry 1 book.

Next geometry lesson