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Quick Start Expectations1. Fill in planner and HWRS HW:
p. 90, #1 (Hint: compare each one to all the others.)
2. Get a signature on HWRS3. On desk: math journal, calculator, textbook,
HWRS, pencil, pen4. Warm Up: Read SS p. 80-81
SS p. 80
Original
Ratios describe and compare shapes.
The rectangle around the original figure is about
10 cm tall and 8 cm wide
The ratio of height (10) to width (8)
is 10 to 8
10 cm
8 cm
Write in your journal:
Write in your journal:
Original 8
10
5
3
8
3 4 6
10 to 8 8 to 3 3 to 6 5 to 4
Can you find any ratios that are equal (equivalent)?Write in your journal:
10 to 8 and 5 to 4 are equivalent ratiosYou can express equivalent ratios with equations.
A proportion is an equation of two equivalent ratios.
Write in your journal:
Journal: 11/24/14Inv. 4: Ratios
• Ratios describe and compare shapes.• The ratio of height (10) to width (8) is 10 to 8• 10 to 8 and 5 to 4 are equivalent ratios• E • TAdd to your journal:• What information does the ratio give you?
A, B, and C are similar!
6 x 1.5 =910 x 1.5 = 15
SF for B to C is 1.5
20 x .75 =15 12 x .75 = 9
SF for A to C is .75
6 x 2 =1210 x 2 = 20
SF for B to A is 2
6 x 1 =610 x 2 = 20SF for B to D is NOT CONSISTENTIF “D” IS NOT SIMILAR TO “B”, IT ISN’T SIMILAR TO “A” OR “C”
Open your book to p. 82
ShortLong
Similar rectangles have the SAME ratio!Non-similar rectangles have different ratios!
Scale Factor:B to A = 2B to C = 1.5C to A = This tells you how many times as great each side length and perimeter are
F and G are similar. They have the same angle measure for corresponding angles. AND, each of the corresponding sides has the same scale factor.
They all have equal ratios:
=
Scale Factor:B to A = 2B to C = 1.5C to A =
Ratio of short side to long side
Similar figures have a constant scale factor and their ratios of corresponding side lengths will be equivalent.
The scale factor gives the amount of stretching (or shrinking) from the original figure to the image.
The ratio of adjacent side lengths within a figure gives an indication of the shape of the original figure (and image), since it compares measures within one figure.
HW: p. 90, #1 (Hint: compare each one to all the others.)
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