"Understanding Triangles" Triangle PPT Courseware 5

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"Understanding Triangles" Triangle PPT Courseware 5

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1. The sum of the three interior angles of a triangle is equal to 180˚.

2. Triangles are classified according to the size of their angles:

⑴ Acute triangle: all three interior angles are acute angles;

⑵Right triangle: One interior angle is a right angle;

⑶ Obtuse triangle: One interior angle is obtuse.

3. The two acute angles of a right triangle are complementary to each other.

test you

1. It is known that ∠A, ∠B and ∠C are the three interior angles of △ABC, ∠A＝70°, ∠C＝30°, ∠B＝( )

2. One acute angle of a right triangle is 70°, and the other acute angle is ( ) degrees.

3. In △ABC, ∠A=80°, ∠B=∠C, then ∠C= ( )

4. If in △ABC, ∠A∠B∠C=2:3∠5, the angle classification of this triangle should be ( ).

Do it

Draw a random triangle on a piece of tissue paper. Can you manage to draw the bisector of one of its interior angles?

Can you get it by origami?

Draw a triangle on a piece of paper, cut it out, and fold one corner of it in half so that both sides overlap.

The crease AD is the angle bisector of the triangle ∠A.

Definition of angle bisector of a triangle:

In a triangle, the angle bisector of an interior angle intersects its opposite side. The line segment between the vertex of the angle and the intersection point is called the angle bisector of the triangle.

∵AD is the angle bisector of △ABC

∴∠ BAD = ∠ CAD =1/2∠BAC

The "midline" of a triangle

In a triangle, the line segment connecting a vertex to the midpoint of the opposite side is called the median of the triangle.

(1) Draw an acute triangle on paper and draw its three midlines.

What is their positional relationship?

Communicate with peers.

(2) Do the three midlines of an obtuse triangle and a right triangle have the same positional relationship?

Fold it, draw it, fold it, draw it,

Summary of this lesson

Through origami, drawing and other activities, students experienced and acquired the concepts and properties of the "angle bisector" and "midline" of a triangle.

In a triangle, the bisector of an interior angle intersects its opposite side. The line segment between the vertex of the angle and the intersection point is called the angle bisector of the triangle.

In a triangle, the line segment connecting a vertex to the midpoint of the opposite side is called the median of the triangle.

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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.

"Understanding Triangles" Triangle PPT Courseware (Lesson 4):

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Update Time: 2024-07-26

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

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