7.1 Angles in Triangles

Key terms


-       Vertex a point where 2 or more points meet

-       Polygon- figure made up of line segments

-       Interior angler an angle made inside a polygon by two lines meeting at a vertex

-       Angle formed outside a polygon by extending of the lines past the vertex- the opposite of it’s interior angle


About Angles in a Triangle


To start of, let’s talk about the properties of angles. When a shape is made, it has a degree. Now this degree is defined by how many sides it has. The shape with the least amount of sides is a triangle. A triangle's degree is 180 degrees.This means that if you measure every angle in a triangle, the sum of those angles will be 180 degrees. Now for a square, since it has an extra side, the total sum of it’s angles will be 360 degrees This is because for every extra side you add starting from a triangle, the total degree of the shape will increase by 180 degrees.



Let’s look at this example. Now we know the sum of all these angles is 180° because of the rule, now if the other two angles are given we can solve for what A is, So if the other 2 angles sum is 120° (60° + 60°), than A is 60, for 180-120=60. Since this is an equalateral triangle, all the angles are equal (60°)


Isosceles triangles have their own properties. in isosceles triangles the two angles at the bottom are always equal, therefore if you solve for one of them you solved for both of them.