"Understanding Triangles" Triangle PPT (Lesson 2)

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"Understanding Triangles" Triangle PPT (Lesson 2)

Part One: Learning Objectives

1. Develop spatial concepts, reasoning skills and organized expression skills through activities such as observation, operation, imagination, reasoning, and communication.

2. Master the relationship between the three angles and three sides of a triangle, and classify triangles according to their sides.

Understanding Triangles PPT, Part 2: Classic Examples

[Example 1] (2019 Xuzhou) The three line segments of the following lengths that can form a triangle are ()

A.2,2,4　B.5,6,12

C.5,7,2 D.6,8,10

[Example 2] The lengths of the four bamboo sticks a, b, c, and d are 2 cm, 3 cm, 4 cm, and 6 cm respectively. If three bamboo sticks are randomly selected and connected end to end to form different triangles, then Triangles share ()

A.1 B.2 C.3 D.4

[Example 3] If the lengths of the two sides of a triangle are 3 and 7 respectively, then the length of the third side may be ()

A.6　B.3

C.2　D.11

[Example 4] It is known that the lengths of the two sides of an isosceles triangle are 2 and 3 respectively, then the perimeter of the isosceles triangle is ()

A.7　B.8

C.6 or 8 D.7 or 8

Understanding Triangles PPT, Part 3: Variation Practice

1. Please write down the length of a set of three line segments that can form a triangle: _________.

2. Each set of numbers below is the length of three wooden sticks. Which one can be used to form a triangle is ()

A.3 cm,4 cm,8 cm

B.8 cm,7 cm,15 cm

C.5 cm,5 cm,11 cm

D.13 cm,12 cm,20 cm

3. The lengths of the two sides of a triangle are 2 and 6 respectively, and the length of the third side is an even number, then the length of the third side is ________.

4. It is known that the lengths of the two sides of an isosceles triangle are 2 and 5 respectively, then the perimeter of the isosceles triangle is ()

A.7　B.9　C.9 or 12　D.12

Understanding Triangle PPT, Part 4: Consolidation Training

5. Taking the following groups of line segments as sides, which triangle can be formed ()

A.2 cm,5 cm,8 cm B.3 cm,3 cm,6 cm

C.3 cm,4 cm,5 cm D.1 cm,2 cm,3 cm

6. It is known that the lengths of the two sides of the triangle are 4 and 10 respectively, then the length of the third side of the triangle may be ()

A.5　B.6

C.12 D.16

7. It is known that the two side lengths of an isosceles triangle are 4 cm and 7 cm respectively, then the perimeter of this triangle is ()

A.15 cm B.18 cm

C. Not sure D. 15 cm or 18 cm

8. It is known that the line segment a=5, b=3, and c is a positive integer, then the triangle composed of a, b, and c as three sides has ()

A.1 B.5

C. Countless D. Unable to determine

9. If the ratio of the lengths of the three line segments is ①1:4:6; ②1:2:3; ③3:3:6; ④6:6:10; ⑤3:4:5, then the ones that can form a triangle are ()

A.1 B.2 C.3 D.4

10. Think about it, can the three line segments in the following questions form a triangle?

(1)6 cm,9 cm,5 cm;

Solution: Because 5+6=11>9, it can form a triangle.

(2)6 cm,8 cm,10 cm;

Solution: Because 6+8=14>10, it can form a triangle.

(3)5 cm,7 cm,5 cm;

Solution: Because 5+5=10>7, it can form a triangle.

(4)12 cm, 3 cm, 7 cm.

Solution: Because 3+7=10<12, it cannot form a triangle.

11. The lengths of the two sides of a triangle are 3 and 5 respectively. Can the length of the third side be 8? Can it be 2? Tell me your reasons.

Solution: The length of the third side cannot be 8, because the sum of the lengths of the other two sides is 8, so the length of the third side must be less than 8, and cannot be equal to 8; similarly, the length of the third side cannot be 2. , because the difference in length of the other two sides is 2, so the length of the third side must be greater than 2, and cannot be equal to 2.

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For more information about the "Triangles and Understanding Triangles" PPT courseware, please click on the "Triangles PPT and Understanding Triangles" PPT tag.

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Update Time: 2024-11-09

This template belongs to Mathematics courseware Beijing Normal University Edition Seventh Grade Mathematics Volume 2 industry PPT template

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