Points distributed on a graph.

Line functions drawn on a graph.

Geometry is a branch of mathematics concerned with questions of shape, size, relative position of figures, and the properties of space. A mathematician who works in the field of geometry is called a geometer.

Points

Points are considered fundamental objects in Euclidean geometry.

Lines

By Euclid's axioms, a line can be drawn from 2 points. Example through 2 points A and B, we can draw the line AB.

A---------------B

Lines of interest

Lines	Definition	Piture
Perpendicular lines	Two lines intecsect at a point to form an angle 90o	${\displaystyle {\overline {AB}}\perp {\overline {CD}}}$
Parallell lines	Two lines do not intecsect each other	${\displaystyle {\overline {AB}}{//}{\overline {CD}}}$
Vector	Line with its direction	${\displaystyle {\vec {AB}}}$

Angles

Two lines intersect at a point to form an angle between 2 lines . Example Line AB intersects line AC to form an angle A between 2 lines. Angle has a symbol ${\displaystyle \angle }$. Angles are measured in degrees (^o) or radians (Rad). Failed to parse (unknown function "\rad"): {\displaystyle \rad}

Example angle 90 degree is π radian

${\displaystyle \angle A=90^{o}={\frac {\pi }{2}}Rad}$

• 
  Acute angle , angle less than 90°
• 
  Right angle , angle equals to 90° (1/4 vòng tròn);
• 
  Obstuse angle angle greater than 90° and less than 180°
• 
  Góc bẹt là góc 180° (1/2 vòng tròn).
• 
  Góc phản là góc lớn hơn 180° nhưng nhỏ hơn 360°
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  Góc đầy là góc bằng 360° (toàn bộ vòng tròn).
• 
  Góc khối
• 
  Đường phân giác
• 
  Chia đôi một góc bằng compa và thước kẻ
• 
  Góc đối đỉnh

Geometric figures

Further reading

•  Calculus
•  Angle