finding and using scale factor

​Corresponding Parts and Scale Factor

​The corresponding angles refer to the angles that are in the same position in each figure.

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Note: These will be EXACTLY THE SAME angle measure.​

​Corresponding Angles

If you are looking at an original figure and a scaled copy, the corresponding sides are the sides in the same position in each figure.​

Note: These will be DIFFERENT​ side lengths.

Corresponding Sides

Corresponding Parts

Corresponding Parts refer to matching parts in each figure. In this case, Johnny's left shoe in the original image corresponds to his left shoe in the scaled copy.​

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​Johnny Bravo is shrinking?!

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Multiple Choice

Which part of the scaled figure corresponds to Johnny's right hand from the original image?

• His right hand!

• His left hand!

• His sunglasses!

Corresponding Angles refer to matching angles in each figure, just like corresponding sides. Even though the scaled copy is smaller, his left fist is making the same angle in both pictures.

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​Johnny Bravo is shrinking?!

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Multiple Choice

Johnny's strong chin in the original image corresponds to his strong chin in the scaled copy.

Which answer choice best describes the relationship between the ANGLES of his chins in both images?

• The angle is WIDER in the scaled copy.

• The angle is NARROWER in the scaled copy.

• The angle is THE SAME as in the scaled copy.

Quadrilateral MNOP is a scaled copy of quadrilateral ABCD. We will use these 2 figures to explore how to use corresponding parts to identify side lengths and the scale factor.​

Corresponding Sides

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In the original image, side AB is the largest side. In the scaled copy, side MN is the largest side.​ This is another way to determine that side AB corresponds to side MN.

Identifying Corresponding Sides

Multiple Choice

Which side in the scaled copy corresponds to side BC in the original image?

HINT: the order of the letters is important!

• side NO

• side OP

• side ON

• side PM

Multiple Choice

Which side in the scaled copy corresponds to side DC in the original image?

HINT: the order of the letters is important!

• side PO

• side OP

• side ON

• side MP

In order to find the scale factor, you must first find a pair of corresponding sides.

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Side AB corresponds to side MN, so we can use these 2 sides to find the scale factor.

Finding the Scale Factor

Finding the Scale Factor

Finding the Scale Factor

In order to use a scale factor, multiply each side length by the scale factor to find the new side length for the scaled copy.

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If the scale factor is 3, then each side will be exactly ​three times as big as in the original image.​ (This means the longest side in your SCALED COPY in this case will be 27 in.)

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Using the Scale Factor

Using the Scale Factor

Multiple Choice

What do we know about the scale figure used to make the smaller image of Johnny Bravo?

• It is less than 1

• It is 1

• It is greater than 1

• There isn't enough information to tell

Multiple Choice

Johnny wants to make a scaled copy of quadrilateral ABCD with a scale factor of 1.8

How will the scaled copy compare to the original image?

• It will be larger

• It will be smaller

• It will be the same size

• There isn't enough information to tell

Multiple Choice

Johnny wants to make a scaled copy of quadrilateral ABCD with a scale factor of 2.

If side GF corresponds to side DC, how long does side GF need to be?

• 8 in.

• 9 in.

• 12 in.

• 18 in.

Multiple Choice

Johnny wants to make a scaled copy of quadrilateral ABCD with a scale factor of 5.

If side GF corresponds to side AD, how long does side GF need to be?

• 11 in.

• 16 in.

• 30 in.

• 36 in.

Angle names can be a little confusing at first. For example, angle DAB refers to the angle in the same corner as point A. The MIDDLE LETTER in the angle name tells you where to find that angle.

Corresponding Angles

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Multiple Choice

Angle MNO can be found between which two sides?

• sides MN and NO

• sides NO and OP

• sides OP and PM

• sides PM and MN

Multiple Choice

Which angle corresponds to angle BCD?

• angle NOP

• angle OPM

• angle PMN

• angle MNO

Multiple Choice

How does angle ABC compare to angle MNO?

• They are the same!

• Angle ABC is smaller than angle MNO

• Angle ABC is larger than angle MNO

• There isn't enough information to tell

Don't close this lesson!

You can move from slide to slide at your own pace, and you can even refer back to these slides and questions to help you on today's assignments if you get stuck.​