- Angles, Lines, and Polygons
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- Measuring an angle with the protractor
- Acute, obtuse, and right angles
- Naming segments, rays, and lines
- Identifying parallel and perpendicular lines
- Acute, obtuse, and right triangles
- Classifying scalene, isosceles, and equilateral triangles by side lengths or angles
- Finding an angle measure of a triangle given two angles
- Naming polygons
- Drawing and identifying a polygon in the coordinate plane

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Triangles can be classified according to their sides or according to their angles. All of each side or angle may be of different or the same sizes; any two sides or angles may be of the same size.

The types of triangles classified by their sides are the following.

**Equilateral triangle** − A triangle with all three sides equal in length is an equilateral triangle. All angles of an equilateral triangle are equal too.

The slash marks indicate equal measure.

**Isosceles triangle** − A triangle in which at least two sides are of equal length is an isosceles triangle.

An isosceles triangle also has two of its angles equal in measure.

**Scalene triangle** − A triangle with all three sides of different lengths is a scalene triangle. The angles of a scalene triangle are also of different measure.

Identify the given triangle as an equilateral, isosceles or a scalene triangle.

**Step 1:**

Given triangle has all sides of same length.

**Step 2:**

So given triangle is an equilateral triangle.

Identify the given triangle as an equilateral, isosceles or a scalene triangle.

**Step 1:**

Given triangle has sides of different lengths.

**Step 2:**

So given triangle is a scalene triangle.

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