standard_description: Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles. For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so.
problem_activity: Problem 1
Pentagon
$${FGHIJ}$$
is a scale image of pentagon
$${ABCDE}$$
.
[IMG]
a.   Complete the table below with the measurements of each pentagon.
| **                Original line segment               ** | **                Original length               ** | **                Corresponding line segment               ** | **                Scale length               ** |
|----------------------------------------------------------|----------------------------------------------------|---------------------------------------------------------------|-------------------------------------------------|
|                          $$AB$$                          |                                                    |                            $$FG$$                             |                                                 |
|                          $$BC$$                          |                                                    |                            $$GH$$                             |                                                 |
|                          $$CD$$                          |                                                    |                            $$HI$$                             |                                                 |
|                          $$AE$$                          |                                                    |                            $$FJ$$                             |                                                 |
b.   Is there a proportional relationship between the side lengths of the original pentagon and the scaled pentagon? Explain using the measurements in the table.
c.   What is the constant of proportionality?
d.   What is the scale factor?
Problem 2
Melissa orders business cards to promote her new website. She previews the cards online before placing her order. The scale image she sees online and the actual size of the cards are shown below.
[IMG]
What scale factor was used to create the online image from the actual size of the business card?
Problem 3
For each situation described below, sketch and label the scale image using the scale factor.
a.   Your family recently had a family portrait taken. Your aunt asks you to take a picture of the portrait using your phone and send it to her. The original portrait is 3 feet by 3 feet and the scale factor from the original picture to the picture on your phone is
$${1 \over18}$$
. Draw the scale drawing, in inches, that would be the size of the portrait on your phone.
b.   Create a scale drawing of the arrow below using a scale factor of 150%.
[IMG]


aligns: no