Geometry - Types of Angles

An angle is formed when two rays meet at a common endpoint. This common point is called the vertex, and the two rays are called the arms of the angle. Visually, think of an angle as the 'opening' between two straight lines that start from the same spot, like the two hands of a clock joined at the center.

Every angle is named using three letters, with the vertex letter always placed in the middle. For example, in $\\angle ABC$, the point $B$ is the vertex where arms $BA$ and $BC$ meet. Visually, the vertex is the corner or 'pointy' part of the angle.

Angles are measured in degrees using a symbol called the degree symbol ($^{\\circ}$). A protractor is the geometric tool used to measure these degrees. It is a semi-circular tool marked with numbers from $0^{\\circ}$ to $180^{\\circ}$ in both directions.

An Acute Angle is any angle that measures more than $0^{\\circ}$ but less than $90^{\\circ}$. Visually, acute angles look 'sharp' or narrow, similar to the letter 'V' or the tip of a sharpened pencil.

A Right Angle measures exactly $90^{\\circ}$. It is special because it forms a perfect 'L' shape, like the corner of a square, a book, or a window frame. Instead of a curved arc, we often mark a right angle with a small square at the vertex.

An Obtuse Angle is an angle that measures more than $90^{\\circ}$ but less than $180^{\\circ}$. Visually, these angles look wide and spread out, like a reclined chair or the roof of a house.

A Straight Angle measures exactly $180^{\\circ}$. It looks like a perfectly straight line with a vertex point in the middle. The two arms of a straight angle point in completely opposite directions, forming a flat surface.

A Zero Angle measures $0^{\\circ}$, where both arms lie exactly on top of each other and no opening is formed. A Complete Angle measures $360^{\\circ}$, which looks like a full circle where the arm has rotated all the way back to its starting position.