My presentation on Triangles for my EDSC 304 Class

1. Triangles
Basic Information and Dimensions
Geometry

2. California Content Standards
 Students’ experience with two-dimensional objects is extended to include
informal explanations of circumference, perimeter and area formulas.
 Use geometric shapes, their measures, and their properties to describe
objects.

3. What are Triangles?
 Triangles are planes or two-dimensional shapes
 They have three sides
 Three angles
 The sum of the three angles has to be 180°
 Can you recall some examples of triangles that you have seen in your life?

4. Types of Triangles
Triangles
Sides
Equilateral Isosceles Scalene
Angles
Right Obtuse Acute

5. Side Type
 Equilateral
 All sides are equal
 All angles are equal at 60°
 Isosceles
 Two sides are equal
 Scalene
 None of the sides are equal

6. Angle Type
 There are three types of triangles based on three types of angles.
 Right triangles
 One angle has to be 90°
 Obtuse triangles
 One of the angles of the triangle has to be more than 90°
 Acute triangles
 All of the angles have to be less than 90°

7. Practice
Name these triangles!

8. Dimension
 So the dimensions we will need to know for a triangle are the three sides, the
base of a triangle and the height. We will use the three sides to find
perimeter but we will use the base side of the triangle and the height to find
the area.
 How do we find base and height?
 Finding Base and Height
 To find the base of a triangle, we can choose one of the sides of the triangle and
make it the base.
 Height on the other hand, there are three ideas to find it.
 Why am I assuming that there are three ideas to find it?

9. Height Explanation
Example 1
It depends on what Triangle we are finding
the height for.
So in this first example we can directly find
the height since the shorter side or leg is the
height of the triangle.
Example 2
In this next example, we do not have our
height directly like the first one, but we
can draw the height from the base to the
upper vertex of the triangle.
Example 3
In this final example, it is not easy to directly
find the height, but we imaginatively extend
the base either left or right to where the top
vertex is, this depends on the side of which
the top is at. Then draw from the base to the
top vertex to get the height.

10. Perimeter
 Perimeter of a triangle is the sum of the sides thus
𝑃𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟 = 𝑠1 + 𝑠2 + 𝑠3
 All triangles apply to this rule, there is a special case for the equilateral
triangle though, this is that since the sides are the same, the perimeter is just
the side multiplied by 3.
 𝑃𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟 = 3𝑠

11. Practice Perimeter Problem
 Let’s say we have this green
triangle with three sides one
measured at 7 centimeters,
another measured at 9 centimeters
and the last one is measured at 14
centimeter. Calculate the
perimeter of this triangle.

12. Area
 This video is from Socratica on
Youtube, which will help explain
the area of a Triangle. Please
watch the video.
 Like in the video the area of a
triangle is 𝐴𝑟𝑒𝑎 =
1
2
∗ 𝑏𝑎𝑠𝑒 ∗ ℎ𝑒𝑖𝑔ℎ𝑡
or 𝐴 =
1
2
𝑏ℎ for short.

13. Practice Area Problem
 Let’s say we have the equilateral
triangle on the left, with the
length of the base is 20
centimeters and the height of this
triangle is 15 centimeters.
Calculate the area of this triangle.

14. To end the lecture….
Any Guesses where famous
triangle this comes from?
There are two references for this.