1. Slideshow 40, Mathematics Mr Richard Sasaki, Room 307
Similar Shapes
Slideshow 40, Mathematics
Mr Richard Sasaki, Room 307

2. Objectives Review how to calculate unknowns in ratios
Understand how to find missing lengths for similar shapes
Calculate missing lengths for similar triangles

3. Ratios
Ratios compare two or more numbers and are written in the form 𝑥 :𝑦 where 𝑥 and 𝑦 are numbers.
Example
If both 4:6 and 10: 𝑥 are in the same ratio, calculate 𝑥.
4:6
x 2.5
x 2.5
10: 15
Easy stuff, try the first worksheet!

4. Answers
Try the activote exercise.

5. Question 1 B A 5cm : 7.5cm 2 : 3 6cm : ____ x 3 x 3 9cm
These two triangles are similar.
7.5cm B
5cm A
6cm ?
Triangle A and B have heights 5cm and 7.5cm respectively.
If triangle A has base 6cm, what is the base of triangle B?

6. Question 2
3cm
3cm
3cm
10cm
9cm
1cm
1. Split the rectangle into 2 similar rectangles that are not congruent.
2. Prove that the flashing length is 3cm using the method in Question 1.

7. Answers
9 cm2
No as only one has an obtuse angle. 4

8. Dissection
Any triangle can be split into four congruent triangles (similar to the original).

9. Puzzle
Watch the picture above carefully…

10. Puzzle Watch the picture above carefully…
Where did the empty square come from?

11. Puzzle
Here it is slower…

12. Solution

13. No!! Solution Are the two triangles similar? 5 : 2 8 : 3 1 : 2/5
1 : 3/8
1 : 0.4
1 : 0.375

14. Answers
Yes, show this with a ruler and measure. The lines make an isosceles triangle.
No, the parallelograms are not similar.
Yes
They are congruent.

15. Counting Answers

16. Counting Answers