Mathematical Reflections on Polygons

In Math, we have been learning about polygons and angles. This post has my answers to some questions about angles and polygons.

1. The common properties of polygons are...
Polygons should have no curves (only lines and vertices), are closed, are 2d figures, and should have no intersecting lines.

My drawing to the left shows these four rules of what a polygon has to be. The first shape has a curve, which means it is not a polygon. Another way to tell this rule is that the number of lines should equal the number of vertices. The shape in the first box has only one line, but but has two vertices.
The second figure is open, which polygons can not be.
The third figure is 3d, and all polygons must be 2 dimensional (length and width).

The fourth figure has intersecting lines, or lines that overlap, and polygons can not have intersecting lines.

2. The measure in degrees in an angle tells me that the angle...
    The measure of degrees in an angle can tell us what type of angle it is. For example, if the angle's measure is 180°, I know it's a straight angle.
        Some of the common angles are...
    Obtuse, acute, right, and straight angles are the most common.

My picture shown above shows the different angles. The first one is an acute angle. All acute angles must be less than 90°. They are the smallest type of angle. Right angles (the 2nd type) must be 90°. Obtuse angles must be between 90° and 180°. Straight angles must be exactly 180°.

3. Some strategies to estimate angle measures are...
    You can use benchmark angles like 45°, 90°, 180°, or 270°. For example, if you are trying to find the measure of an angle that is 85°, you will notice that it is slightly smaller than a right angle. So you might assume that it is somewhere between 80 and 90 degrees.

        To find accurate measurements with tools, I should...
    When you are measuring lines, angles, or any other geometrical shape, it is very important to line things up. For example, while measuring an angle, the 0 line on your protractor should line up with the initial side of the angle. If you are measuring a line, you should make sure that the 0 mark on the ruler matches up with the beginning of the line. This also means that the end of the geometrical figure should match up. So in an angle, the terminal side is on a line, and in a line the ruler is matched up with the end of the line. This is important because you can get really different answers if you don't do this. For instance, if you don't line it up, a 10° angle can become a 100° angle.
    While measuring angles, you also want to know which number to look at. This is because the measure for an angle greater than 180° is written above the measure for an angle less than 180°.