Triangle or triangle is the name of a form made from three sides which are straight lines and three angles. Mathematician Euclid who lived around 300 BC found that the sum of the angles in a triangle on a plane is 180 degrees. To prove that the angles in a triangle is 180 degrees, then how much can be done, including:
1. Proof using a measuring instrument angle or protractor.
This is the most simple and easy way if we have a protractor.
Suppose we had any triangle as shown above, and given the name of each vertex, namely A, B and C.
In the triangle are the angle CAB, ABC angle, and the angle ACB.
By using a protractor each - each measured and calculated angle large angle.
After that, the three angles added together and the result will amount in 1800
CAB + ABC + ACB = 180
2. Proof by extending a line from one side.
In the triangle are the angle CAB, ABC angle, and the angle ACB.
By using a protractor each - each measured and calculated angle large angle.
After that, the three angles added together and the result will amount in 1800
CAB + ABC + ACB = 180
2. Proof by extending a line from one side.
First create arbitrary triangle. Each vertex is named. Let A, B and C.
Create a line extension at any point. Let point C in line with AC.Lalu we give a point and the name is D so we got a line CD.Melalui point C, draw a line parallel to AB. After the given point and which is E, produced a line CE.Sehingga line AB || CE line in the opposite angle ABC to the angle BCE, so the angle ABC = angle BCE
Sehadap angle BAC to the angle DCE, so the angle BAC = angle DCE.
And we can see and conclude that the angle ACB + + DCE = 180 BCE.
3. Proof with the help of a line parallel to one side.
Create a line extension at any point. Let point C in line with AC.Lalu we give a point and the name is D so we got a line CD.Melalui point C, draw a line parallel to AB. After the given point and which is E, produced a line CE.Sehingga line AB || CE line in the opposite angle ABC to the angle BCE, so the angle ABC = angle BCE
Sehadap angle BAC to the angle DCE, so the angle BAC = angle DCE.
And we can see and conclude that the angle ACB + + DCE = 180 BCE.
3. Proof with the help of a line parallel to one side.
Draw a line parallel to the sides AB and through point C, name the line DE.
CAB opposite corner in the corner of the ACD, the angle CAB = angle ACD = X
ABC opposite corner in the BCE angle, the angle ABC = angle BCE = Y
And a large angle ACB is Z
So the number of ACD + angle ACB + BCE = X + Y + Z = 180
4. Proof With Cutting / cutting Each vertex
The stages as following:
- Cut each titiksudut
- Connect all the vertex so be
