Lines and Angles

There are 4 main types of angles: acute, right angle, obtuse angle and straight angle. 

If the angle is less than 90 degrees, it is acute angle

If the angle is 90 degrees, it is a right angle 

If the angle is more than 90 degrees, it is an obtuse angle 

If the angle is 180 degrees, it is a straight angle


The sum of the angles of a straight line is 180 degrees

If you have a full circle, the measurement of the angles around the point is 360 degrees.
Angles that face each other (vertical angles) are congruent.

(A and D or B and E) are equal to each other.

Vertical angles are congruent (equal to each other), then:
For example: angle FOE is vertical to BOC
Moreover, to solve Y,FOA is also
Vertical to COD then:
COD=2(30)=60°, AOF=3(30)-30=60°

Finally, to find Z, we know EOB is straight angle,


When two parallel lines are crossed by another line
(called the transversal).
You need to remember which angles are equal to each other.

Let's Practice

Let's Practice

Let's Practice

If two angles are supplementary they make up a single straight line, also the sum of their measures is 180°
If two angles are complementary they make up a right angle, also the sum of their measures is 90°
A good way to remember is that

Complementary is a Corner of 90 degrees



Supplementary and Complementary Angles

 Parallel Lines


A triangle is a closed figure with 3 sides.
The sum of the interior angles of any triangle is 180 degrees.

There are three different types of triangles depending on the sides and angles.
Let's see the different types of triangles and their properties:

Types of Triangles 

Right Triangles