Plane geometry is the study of figures on a two-dimensional surface — that is, on a plane. You can think of the plane as a piece of paper with no thickness at all. Technically, a plane doesn’t end at the edge of the paper but rather continue without ending.
ANGLES
An angle is formed when two lines intersects.Angles are typically used in carpentry to measure the corners of objects. They’re also used in navigation to indicate a sudden change in direction. For example, when you’re driving, it’s common to distinguish when the angle of a turn is “sharp” or “not so sharp.”

TYPES OF ANGLES

ACUTE ANGLES
They are angles that are lower than 90 degrees — that is, angles that are sharper than a right angle .

OBTUSE ANGLES 
They are angles that measure greater than 90 degrees but lower than 180 degrees— that is, angles that aren’t as sharp as a right angle. Diagram is shown below

 RIGHT ANGLES
They are angles that are equal to 90°.That is the most common angle type.
Diagram is shown below........

REFLEX ANGLES
They angles greater than 180° but less than 360°. Acute or obtuse angles is added to reflex angle to form a full circle.

COMPLEMENTARY ANGLES
They are angles that sum up to 90°. That means if angle a° is added to angle b° and it is equal to 90°,then they are called complementary angles. 
SUPLEMENTARY ANGLES
They are angles that sum up to 180°. That is angle A° + B° = 180°. Diagram is shown below.

VERTICALLY OPPOSITE ANGLES 
The angles opposite each other when two lines cross. They are always equal. In this example a° and b° are vertically opposite angles.
ANGLES ON A STRAIGHT LINE 
Angles on a straight line sum up to 180°. They almost like supplematry angles.

ANGLES ON A POINT
An angle is measured with reference to a circle with its centre at the common endpoint of the rays. Hence, the sum of angles at a point is always 360 degrees.


Click on the link below to watch a video tutorial on plane geometry............
https://youtu.be/kiR8N5s230k
ASSIGNMENT

Calculate the size of each angles marked with letters in the diagram below.