Angles are measured in degrees from 0 to 360, representing a full rotation around a point. Starting at 0 degrees, the angle increases as you move around a circle.

• From 0 to 90 degrees, angles are called acute angles. These angles are sharp and less than a right angle.
• At exactly 90 degrees, the angle is called a right angle. It represents a perfect corner, like the corner of a square.
• Angles greater than 90 degrees but less than 180 degrees are called obtuse angles. These angles are wider than a right angle but less than a straight line.
• At 180 degrees, the angle is called a straight angle, forming a straight line.
• Angles between 180 and 360 degrees are called reflex angles, which are larger than a straight angle but less than a full circle.
• Finally, 360 degrees represents a full rotation, bringing you back to the starting point.

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 /  60°
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This simple ASCII diagram represents an angle of 60 degrees. The angle is formed between the horizontal line at the bottom and the slanting line above it.

Transversal and the Relationship Between Angles Formed by a Transversal Across Two Parallel Lines

When a transversal is drawn across two parallel lines, several angles are formed at the points of intersection. These angles have specific relationships that are fundamental in geometry.

Key Angles Formed:

• Corresponding Angles: These are pairs of angles that occupy the same relative position at each intersection where the transversal crosses the parallel lines. For example, the angle at the top left of the first intersection and the angle at the top left of the second intersection.
• Alternate Interior Angles: These angles lie between the two parallel lines but on opposite sides of the transversal. For example, one angle might be on the left side of the transversal at the first intersection, and the other on the right side of the transversal at the second intersection.
• Alternate Exterior Angles: These angles lie outside the two parallel lines and on opposite sides of the transversal.
• Consecutive Interior Angles (or Co-Interior Angles): These angles are on the same side of the transversal and lie between the two parallel lines.

Relationships Between Angles:

• Corresponding Angles are equal.
• Alternate Interior Angles are equal.
• Alternate Exterior Angles are equal.
• Consecutive Interior Angles are supplementary (their measures add up to 180 degrees).

These relationships help prove that the lines are parallel and are used to solve for unknown angle measures in geometric problems.