Quick Start Expectations1. Pick up new HWRS and fill in

HW: SS p. 38-42 #5-7, #16-172. Get a signature on HWRS3. On desk: journal, HWRS, pencil, pen4. Warm Up:8 + (16 – 12) + (2 x –5) = –(3)² + 9(7 x –2) =

Inv. 2.3

Teacher Note:It will save time to give half the class the rectangles (Section A, 1-4) to work with and half the class the triangles (Section B, 1-4.) Then have team report out their findings.

Rectangles (mouths) J, L, and N are similar.

All angles are right angles, or the same size, so you only need to check the side lengths.

Scale factors (small to large): L to J = 2L to N = 3J to N is = 3/2

Scale factors (large to small): J to L = ½ N to L is = 1/3 N to J is = 2/3 Reciprocals!

Perimeters:J = 20L = 10N = 30

Area: J = 16L = 4N = 36

The perimeter of the larger rectangle is the scale factor times the perimeter of the smaller rectangle. (You have increased all sides by the same factor!)

The area of the larger rectangle is the “square of the scale factor” times the area of the smaller rectangle.

Triangles (noses) O, R, and S are similar to each other.

Scale factors (small to large): O to R = 2O to S = 3R to S = 3/2

Scale factors (large to small): R to O = ½ S to O is 1/3S to R is 2/3Reciprocals!

Area: O = 1R = 4S = 9

Yes! The area of the larger triangle is the “square of the scale factor” times the area of the smaller triangle. The scale factor from O to S is 3 and nine triangle Os fit into triangle S. (3x3 = 9 = )

The first 2 triangles are similar because the scale factor for each pair of corresponding sides is constant (2) and the corresponding angles are equal.

The factors from any side of the first 2 triangles to the corresponding side of the third triangle are all different, so the third triangle is NOT similar to either of the first two.

One team from mouths and one team from noses report out.

Both of them are correct! Determining scale factor depends on whether you are going from the larger figure to the smaller, or from the smaller figure to the larger.The scale factor from L to J is 2 and from J to L is 0.5 or ½ .

Divide the length of the second figure by the corresponding length in the first figure, or find a number that the length of the first (original) figure is multiplied by to get the corresponding length in the second figure (image).

Divide the length of the second figure by the corresponding length in the first figure.

Or…

Find a number that the length of the first (original) figure is multiplied by to get the corresponding length in the second figure (image).

NO! Using a constant scale factor to stretch or shrink sides does not change the angle size.

Coordinate Graphs –This is exactly the same as saying that (x, y) has been transformed into (2x, 2y). The scale factor is 2.