There are many math learning materials at school that your little one might learn, Mother. One of them is a triangular flat shape.
Flat shapes are flat objects or planes that are flat and only have two sizes or two dimensions. The lines that form a plane figure are called sides and the areas formed by the intersection of the lines are called angles.
Summarizing from the book Math 4 by Dian Amalia and Imam Wahyudi, there are regular and irregular shapes. The lengths of the sides and the angles that form them have no particular pattern or characteristic. For example, such as torn paper, broken plywood, and so on.

The naming of flat shapes is usually adjusted to the number of sides, corner points, to the distinctive properties it has.
Flat wake transformation
Flat shapes can undergo transformation on changes in location or shape. This happens when the flat shape is rotated (rotated), shifted (translation), reflected (reflection), and enlarged or reduced (dilated).
Rotation of the plane figure is rotated about an axis at one of the corner points. The translation of the plane figures is done by shifting all the points of the plane figures in one direction, so that their positions move.
Flat shape dilation is a flat shape that is changed or transformed by increasing or decreasing the size of its sides. In this transformation, the concepts of comparison and scale apply, Mother.
Congruence and similarity wake up flat
Similarity is two flat shapes that have the same angles and the side lengths are in the same ratio. Meanwhile, congruence is two flat shapes that have the same size angles and side lengths. It can also be said to be the same and congruent.
Congruent flat shapes are definitely congruent. Meanwhile, flat figures that are congruent are not necessarily congruent.
Rotation, translation, and reflection plane shapes will have the same side and angle sizes. That way, the resulting flat shape is congruent with the original flat shape.
Meanwhile, the dilated shape has the same angle size, but the length of the sides is increased or decreased from the original flat shape. Even so, the resulting flat shapes are congruent.
Flat wake properties
There are several properties of flat wakes that need to be considered, Mother. Here is the row:
 The area bounded by 3 line segments is called a triangle.
 The area bounded by 4 line segments is called a quadrilateral.
 The area bounded by 5 line segments is called a pentagon, and so on.
The number of line segments and the model that a shape has is one of the properties of the flat shape. So, the nature of a plane figure is determined by the number of segments, lines, line models, and angles.
Build a flat triangle
Flat triangles are often found in everyday life, Mother. For example, pizza shapes, traffic signs, tents, hangers, to rulers.
One of the flat shapes that is often learned at the Little One’s school is a triangular flat shape. A triangular shape is a flat shape formed by three intersecting straight lines.
The sum of the angles of a triangle is 180 degrees, Mother. This angle is formed by the number of sides.
Triangle type
There are various types of triangles, ranging from angles to side lengths. Types of triangles based on the size of the angles include acute triangles, right triangles, and obtuse triangles. While the triangles based on the length of the sides are isosceles triangles, equilateral triangles, and arbitrary triangles.
1. Triangles based on the size of the angles
Quoting from the book Learning Mathematics in Elementary School by Siti Ruqoyyah, the following is an explanation of the types of triangles based on the size of the angles:
Acute triangle
The first type of triangle based on the size of the angle is an acute triangle, Mother. An acute triangle is a triangle in which each angle is less than 90 degrees.
Right triangle
A right triangle is a type of triangle in which one angle is 90 degrees. Look at the picture of the right triangle below, yes, Mother.
Right Triangle/ Photo: Math Book 4

obtuse triangle
The third type of triangle based on the size of the angle is an obtuse triangle. This triangle has one angle that is greater than 90 degrees.
2. Triangle based on side length
The following is a description of the types of triangles based on the length of their sides, Mother:
Isosceles triangle
The first type of isosceles triangle is an isosceles triangle. This triangle has a pair of sides that are the same length. Its characteristics are as follows:
 Formed from two congruent right triangles.
 It has two equal sides and two equal angles.
Equilateral triangle
The type of equilateral triangle is a triangle where each side is the same length, Mother. Following are the characteristics of an equilateral triangle:
 Have the same angle.
 The sides are the same length.
 The four special lines of the triangle coincide and divide the angle into two equal parts.
 The special lines of an equilateral triangle are the axes of symmetry. The number of axes of symmetry in an equilateral triangle is 3.
 An equilateral triangle occupies its frame in six ways.
Any triangle
Any triangle is a triangle whose three sides have different sizes, Mother. Its properties are as follows:
 Does not have equal sides.
 The three angles are not equal.
The formula for the perimeter of a triangle
The perimeter of a triangle has the formula for the sum of the lengths of the three sides of a triangle. So, you only need to add up all the sides of the triangle.
Problems example
1. Triangle ABC has the following side lengths:
AB = 6 cm, BC = 5 cm, CA = 3 cm
What is the perimeter of triangle ABC?
Answer:
Perimeter of triangle ABC = Sum of the lengths of the three sides
AB + BC + CA
6 cm + 5 cm + 3 cm = 14 cm
2. Right triangle ABC has the following side lengths:
AB = 3 cm, BC = 4 cm, CA = 2 cm
Find the perimeter of the right triangle ABC.
Answer:
Perimeter of triangle ABC = Sum of the lengths of the three sides
AB + BC + CA
3 cm + 4 cm+ 2 cm = 9 cm.
3. It is known that a triangle has sides that measure 10 cm, 8 cm, and 6 cm. How many triangles are…
Answer:
Perimeter of triangle = sum of three sides
= 10 cm + 8 cm + 6 cm
= 24 cm
The formula for the area of a triangle
Area Formula for Triangle/ Photo: Math Book 4

Build a triangular space with a height called a line height, Mother. The height of a triangle is the length of the line segment drawn from the vertex of the triangle and perpendicular to the line containing the opposite side.
The formula for the area of a triangle is base x height divided by 2, Mother. Or it could be with the formula 1/2 x base x height.
Problems example:
1. We know that an acute triangle has a base of 10 cm and a height of 8 cm. Calculate the area of the triangle.
Answer:
Area of triangle = base x height : 2
= 10 x 8 : 2
= 80 : 2
= 40 cm squared
2. Triangle ABC has a base of 20 cm and a height of 25 cm. What is the area of triangle ABC?
Answer:
Area of triangle = base x height : 2
= 20 cm x 25 cm : 2
= 10 cm x 25 cm
= 250 cm squared
3. It is known that a triangle has a base of 8 cm and a height of 6 cm. What is the area of the triangle?
Answer:
Area of triangle = base x height : 2
= 8 cm x 6 cm : 2
= 8 cm x 3 cm
= 24 cm squared.
Mother, come on download Allo Bank digital app here. Get 10 percent discount and cashback 5 percent.
Don’t forget to also take a look at the video tips for children to be comfortable hanging out at school below:
(mua/for)