Coaching Centre
Measuring and classifying angles
Using a protractor, and classifying angles as acute, right, obtuse, straight, reflex or a revolution.
Types of angles
The angle between the positive x-axis and the coloured arm. Drag the slider to see each type.
Find where the angle changes from acute to obtuse.
Using a protractor
- Put the centre of the protractor on the vertex.
- Line up the zero line with one arm.
- Read the scale that starts at $0^\circ$ on that arm.
Reflex angles
A protractor only goes to $180^\circ$. To find a reflex angle, measure the smaller angle and subtract from $360^\circ$.
The smaller angle at a vertex is $125^\circ$. Find the reflex angle.
What angle does the minute hand turn through in $20$ minutes?
An angle of $134^\circ$ is:
It is between $90^\circ$ and $180^\circ$.
An angle of $200^\circ$ is:
Between $180^\circ$ and $360^\circ$.
The smaller angle is $125^\circ$. Find the reflex angle.
$360 - 125$.
How many degrees does a minute hand turn in $20$ minutes?
$6^\circ$ per minute.
How many degrees are in a right angle?
A quarter turn.
An angle of $89^\circ$ is:
Less than $90^\circ$.
What angle is three quarters of a revolution?
$\tfrac{3}{4} \times 360$.
What is the smaller angle between the hands of a clock at 5 o'clock?
$5$ hour gaps of $30^\circ$ each.
New numbers every time. Keep going until you get five in a row.