"Skillful Little Craftsman" PPT Courseware 2

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"Skillful Little Craftsman" PPT Courseware 2

1. Situation introduction

There are 4 small sticks, the lengths are 2cm, 3cm, 5cm and 6cm respectively.

Can any three small sticks form a triangle?

What mathematical information do you know from the picture?

What questions can you ask based on this information?

2. Cooperation and exploration

Can any three small sticks form a triangle?

Exploration activity requirements:

1. Select any 3 of the 4 small sticks and try to form a triangle.

2. Record the results of the investigation in the table below.

What is the relationship between the three sides of a triangle?

As a group, discuss and communicate based on the situation surrounding the triangle and find out the relationship between the three sides of the triangle.

Draw it, measure it, do the math, what conclusion can you draw?

Operational requirements:

Each person draws a triangle, measures the lengths of the three sides, and calculates whether the sum of any two sides of the triangle is greater than the third side.

in conclusion:

The sum of the lengths of any two sides of a triangle is greater than the third side.

Can you use letters to express the relationship between the three sides of a triangle?

� + b > c

b + c > �

� + c > b

3. Independent practice

1. Can the three sticks in each group form a triangle?

Think about it, how can you quickly determine whether three line segments can form a triangle?

A triangle can be formed as long as the sum of the two shorter sides is greater than the third side.

2. How many decimeters (rounded to the nearest decimeter) long wooden strip can be used to nail it into a triangle?

According to the relationship between the lengths of the three sides of the triangle:

� + 8 � 12

8 + 12 � �

Therefore, the length of the third side must be greater than 4 and less than 20.

Answer: Take another piece of wood longer than 4dm and less than 20dm and nail it into a triangle.

3. Which group of small sticks can form an isosceles triangle in a row.

4. He obviously wants to build a house for his puppy. The roof frame is triangular. One of the wooden bars is 5 decimeters long and the other wooden bar is 3 decimeters long. So how many decimeters can the third wooden bar be? (rounded to decimeters)

5, 3, 7

5, 3, 6

5, 3, 5

5, 3, 4

5, 3, 3

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Update Time: 2024-08-31

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