Angles in a triangle part two
Another way to show that the angles in triangles add up to 180° is to consider the number of degrees in a square or a rectangle.
In a square there are four angles of 90°.
The four angles inside a square add up to 360°.
90 + 90 + 90 + 90
= 180 + 90 + 90
= 180 + 180
= 360
If we draw a line between two opposite corners of the square then we will create two triangles. The angles in each triangle will add up to half the total in a square. This is 360 ÷ 2 = 180.
This is also true of a rectangle:
