Mathematical thinking clearance
Grade 4 Lecture 9 Triangle Corner Relationship
Knowledge points: 1. The sum of the inner angles of the triangle is 180°.
Classification by angle: acute triangle, right triangle, obtuse triangle.
2. Sides of the triangle: The sum of any two sides of the triangle is greater than the third side.
The difference between any two sides of the triangle is less than the third side.
Classified by edge: equilateral triangles (regular triangles), isosceles triangles, unequal triangles.
3. The relationship between the edge and the angle: in the same triangle, the big side is against the big angle;Equilateral to equilateral.
4. Special triangles: equilateral triangles (regular triangles), isosceles right triangles.
Special angles: 60°, 45°, 90°, 135°
5. The sum of the inner angles of the n-sided shape: (n 2) 180°
1. The three line segments of the following lengths can form a triangle ( ).
a．1cm，2cm，5cm b．4cm，5cm，9cm
c．5cm，8cm，15cm d．6cm，8cm，9cm
If an isosceles triangle is 2 and 5 long, its circumference is ( ).
a 7 b 9 c 12 d 9 or 12
Knowing that the two sides of a triangle are 3 and 8 long, then the length of the third side of this triangle may be ( ).
a． 4 b．5 c． 6 d． 13
Grade 4 Lecture 9 Triangle Corner Relationship (1).Mathematical thinking clearance
Grade 4 Lecture 9 Triangle Corner Relationship
2. As shown in the figure, the triangle is an isosceles right triangle, thendegrees,degrees,degrees,
Click (up to 18 words) as shown in the figuredegrees,
Grade 4 Lecture 9 Triangle Corner Relationship (2).Grade 4 Lecture 9 Triangle Corner Relationship
3. As shown in the figure, the 8 inner angles of the octagon are all 135°, and AB ef, BC 20, de 10, fg 30, then ah
Grade 4 Lecture 9 Triangle Corner Relationship (3).