Types of Aangles (Right, Acute, Obtuse, Flat): Adding / subtracting angles

To solve this problem, we need to recall the definition of a right angle.

A right angle is defined as an angle that measures exactly $90^\circ$. This is a standard definition found in geometry, describing an angle formed by the intersection of two perpendicular lines.

Given the multiple-choice options, we need to identify which one corresponds to a right angle:

• A right angle measures $90^\circ$.

Let's examine the provided choices:

1. Angle of 180°.
2. Minor angle of 90°.
3. Angle of 90°.
4. Angle greater than 90°.

Choice 3, "Angle of 90°," directly matches the definition of a right angle.

Therefore, the correct answer is Angle of 90°.

To solve this problem, let's begin by understanding what a flat angle is:

• A flat angle is an angle that measures exactly $180^\circ$.
• Visually, you can think of a flat angle as a straight line, where the two arms of the angle lie on opposite sides of the vertex, forming a straight angle.
• It is larger than a right angle, which measures $90^\circ$, and exactly twice the measure of a right angle.
• Flat angles are often used to understand the concept of supplementary angles, where two angles sum up to create a flat angle of $180^\circ$.
• None of the sides of a flat angle are considered to turn; they continue in a straight direction.

Among the given choices, the option that correctly defines a flat angle is the one that states, "Angle of 180°."

Therefore, the solution to the problem is that a flat angle is an angle of $180^\circ$.