Perimeter, Circumference, & Area

Objectives: - Find the perimeter and area of common plane figures - Use a general problem solving plan.

But first, let’s review angles . . .

Reviewing perimeter & circumference

Square 4s Rectangle 2l + 2w Triangle a + b + c Circle (circumference) 2πr

Reviewing area

Square s2

Rectangle lw Triangle 1/2 bh Circle πr2

Rectangle

Get graph paper and draw a 5 by 12 rectangle.

Perimeter = 2 l + 2 w = 2*12 + 2*5 = 34Area = lw = 12*5 = 60

Circles

Consider a circle with a diameter of 8 cmWhat is the radius?Circumference = 2πr = 2*3.14*4 = 2.51 cmArea = πr2

= 3.14*4*4 = 50.2 cm2

Example 3 - Triangle

Get graph paperDraw x & y axisPlot points D (1,3) E (8,3) and F (4,7) Draw the height from point F to side

DE.Label the point where the height

meets DE as G.

Example 3

How long is the base? 8 - 1 = 7How high is the triangle? 7 - 3 = 4A = 1/2 base * heightA = 1/2 * 7 * 4A = 14 square units

A Problem-Solving Plan

Ask yourself what you need to solve the problem. Write a verbal model or draw a sketch that will help you find what you need to know.

Label known and unknown facts on or near your sketch.

Use labels and facts to choose related definitions, theorems, formulas, or other results you may need.

Reason logically to link the facts, using a proof or other written argument.

Write a conclusion that answers the original problem. Check that your reasoning is correct.

Example

Look at page 53.Notice the verbal model, labels, &

reasoningCheck the unitsLook at examples on p. 54Follow these guidelines on the test

Try problems 3 - 8

Homework: worksheets