# What is the scale factor in relationship to similarity

### Similarity (geometry) - Wikipedia Usually I am used to finding scale factor by dividing two sides but since no sides are given, I'm not sure how to find it. – Sujaan Kunalan Jun 5. The scale factor describes the relationship between the two similar triangles. of an individual triangle; their values have nothing to do with the similarity of the. How can we use the relationship between area and volume to help us Scale Factor: The ratio of the lengths of the corresponding sides in.

We can also solve many other practical problems involving matters such as graphs, floor plans, scale drawings, and maps. I want you to find the different pairs of shapes indicated on your record sheet and group them together.

## Using similarity

You will be comparing these pairs of figures. As a group you will look at one pair at a time. Brainstorm as many ideas as you can about how the figures compare. Think about how all of the corresponding parts compare.

Write a specific comparison statement involving the corresponding sides and angles in the space provided. Repeat these steps until you have compared all of the pairs.

Similar Polygons and Scale Factors: Examples (Basic Geometry Concepts)

Give a warning when work time is nearing an end. Gauge this on when you see most groups finishing the last comparison around 10—12 minutes. As you circulate, pay attention to the variety of statements the groups have written. Make note of statements you want students to share with the class.

Some of the statements may be excellent; others may need some work. As responses are shared for each pair, bring up ideas that may help to more accurately compare the figures. Be sure to mention the need to compare the ratios of corresponding sides. After all of the shape pairs have been discussed, bring up congruence and similarity: Can you name them?

We have a special symbol to represent congruence; it looks like an equal sign with a squiggle above it. Can I have a volunteer to remind us of how we know these figures are congruent? If there are any pairs that are proportional in size they are called mathematically similar. Please label them on your record sheet.

### Congruency, Similarity, and Scale Factor - SAS

The characteristics you are looking for are the same general shape, pairs of corresponding sides that all have the same ratio, and pairs of corresponding angles that are all congruent.

Can someone explain why? Ask students several questions to check for understanding before moving to the next activity. This gave us the information we needed to determine if the figures were congruent, mathematically similar, or neither.

There is another piece of information that is very helpful in comparing figures, solving problems, and making detailed drawings of all sorts including maps. This is the scale factor. We already considered everything we needed to figure out scale factor in our last activity. Did anyone write that your ratios were 8: If you looked at A first and compared it to B, which is larger, you used 4: If, on the other hand, you looked at B first and compared it to A, which is smaller, you would have stated 8: For figures A and B our scale factor is 2 if we look from small A to large B because each side needs to be multiplied by 2 to create the enlarged figure.

### Scale Factors and Similarity - Math Concepts Grade 9

But, if we wanted to go from B to A, this would be reducing the size of the square so we would multiply by to get the reduced figure size. Emphasize these key concepts: It is important to know if you are going from small to large enlargement or large to small reduction.

When two figures are compared, the figure labeled without prime symbols is the original figure A, B, C, D. The figure labeled with prime symbols is what you are transforming into, and it is considered the image A', B', C', D'.

In congruent and similar figures, all pairs of corresponding angles are always congruent and never change because of the scale factor of the sides. Scale Factor and Similarity Graphing Activity For this activity, students should work individually or in pairs.

They will plot several points, which are provided on the activity sheet. The points need to be connected in order and labeled with the indicted letters. For each problem, two similar polygons will be formed on each coordinate axis. Students will use the grid squares to label the side lengths all around both figures. They will determine the scale factor of the sides, the perimeter and area of each figure.

Allow approximately 15—20 minutes to work, but be flexible based on student needs. Assist students who may need further direction. Ask students who seem very proficient to explain the relationship between the perimeters of one pair of similar figures, or the relationship between the areas of one pair of similar figures. Two sides have lengths in the same ratio, and the angles included between these sides have the same measure.

This is known as the SAS similarity criterion. Any two equilateral triangles are similar. Two triangles, both similar to a third triangle, are similar to each other transitivity of similarity of triangles. Corresponding altitudes of similar triangles have the same ratio as the corresponding sides. Two right triangles are similar if the hypotenuse and one other side have lengths in the same ratio. The statement that the point F satisfying this condition exists is Wallis's postulate  and is logically equivalent to Euclid's parallel postulate.

In the axiomatic treatment of Euclidean geometry given by G. Birkhoff see Birkhoff's axioms the SAS similarity criterion given above was used to replace both Euclid's Parallel Postulate and the SAS axiom which enabled the dramatic shortening of Hilbert's axioms. Among the elementary results that can be proved this way are: Similar triangles also provide the foundations for right triangle trigonometry.

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