Angles – ‘Acute’, ‘Obtuse’ and ‘Reflex’
We have learnt about a right angle and a straight angle. However, as seen in the case of the angles made by the hands of a clock, in most cases the angles we come across in real life, are different from these two kinds.
Say, the angle made by a ladder slanted on the wall (or with the floor) is neither a right angle nor a straight angle. How to work with such angles?
What are the angles smaller than a right angle?
And the angles greater than a right angle?
Using right and straight angle as references, we make a classification:
An angle smaller than a right angle is called an
If an angle is larger than a right angle, but less than a straight angle, it is called an
A
Select a point Acute and drag towards Obtuse and drag towards Reflex.
Making a Tester
To help classify the different angles into the categories of - acute, obtuse, right and reflex, we have a primitive way of doing it.
Tear an appropriate size of paper in the shape of a square, such that we can handle it conveniently during measurement and fold it along one of its side. This piece of paper is represented by the rectangle 1234. Join the points "A" and "B"
which are the midpoints for the shown rectangle side.
We now have the rectangle 12BA. We take the mid-points "C" and "D" and join them.
After that, make another fold starting from the middle of the folded edge and fold along the other side. This is a "tester" which helps in finding out whether an angle is right angle or less/more than that.
When using, align one of the straightened edges of the tester with that of the arms of the angle. If the arm of the angle is beyond the alignment of the other edge of the tester, the angle being measured is
If the arm of the measured angle, lies within the edges of the tester, the angle is
If the arm aligns with both the straightened edges of the tester then, the angle being measured is a
Paper folding task
Step:1 Fold a sheet of paper in half
Step:2 Without unfolding the paper fold it in half again (click on the second paper to split it).
Step:3 Fold the paper in half one more time.
Exercise
Match the following