NCERT Solutions for Class 4th Maths Chapter 1 Drawing acute and obtuse angles; marking angles in figures — Let Us Do
Book page 13 Updated on2026-09-19
Q1.
Draw some acute angles on the top grid. Draw a line to make an acute angle using each given line in the bottom grid.
The two grids of the left-hand box. Two lines are already drawn in the lower grid.
Answer
An acute angle must be smaller than a right angle, so keep the two arms
close together.
On the top grid
Pick a dot for the corner.
Draw one arm going across, say 4 dots to the right.
Draw the second arm going 4 dots to the right but only 1 dot up.
The two arms stay close, so the angle is acute. Check with your paper checker —
it should be narrower than the checker’s corner.
On the bottom grid — two lines are already drawn there.
For the slanting line, start at its upper end and draw a new line that
goes down in nearly the same direction, only a little apart from it.
For the straight standing line, start at its top end and draw a line going
down and only slightly to one side.
Why it happens: The closer the two arms lie to each other, the
smaller the opening between them — and a small opening is an acute angle.
Q2.
Draw some obtuse angles on the top grid. Draw a line to make an obtuse angle using each given line in the bottom grid.
The two grids of the right-hand box. Two lines are already drawn in the lower grid.
Answer
An obtuse angle must be wider than a right angle, so open the two arms out
well.
On the top grid
Pick a dot for the corner.
Draw one arm straight up, 3 dots.
Draw the second arm going 4 dots to the right and 2 dots down.
The arms are now more than a quarter turn apart, so the angle is obtuse. Check with
your paper checker — it should be wider than the checker’s corner.
On the bottom grid
For the standing line, start at its lower end and draw a line going
sideways and a little downwards.
For the slanting line, start at its lower end and draw a line going the other
way, opening it out well past a square corner.
Why it happens: The wider the two arms swing apart, the bigger
the opening. Once the opening passes the corner of a square, the angle is obtuse.
Q3.
In the figures given below, mark the acute angles in red, right angles in green, and obtuse angles in blue.
The four stick figures printed in the book.
Answer
Test every joint of each stick figure with your paper right angle checker,
then colour the mark.
If the corner is narrower than the checker → mark it red
(acute).
If it fits the checker exactly → mark it green (right angle).
If it is wider than the checker → mark it blue (obtuse).
Where to look in each figure
at the neck, where each arm leaves the body;
at the elbow, where the arm bends;
at the hip, where each leg leaves the body;
at the ankle, where a foot rests on the ground line.
Sample answer: In the figure with both arms raised, the two
arms make an acute angle with the body; in the figure with arms stretched
sideways, each arm makes about a right angle; in the figure with arms hanging
down and legs wide apart, the legs make an obtuse angle at the hip.
Why it happens: The angle depends only on how far the two parts
have swung apart, so the same joint gives a different angle in each figure.