Acute angles are less than a right angle. Name some objects from your classroom which have an acute angle. ________________________________________________________. acute angle obtuse angle The two angles drawn in the book. The dotted arm shows where a right angle would be.

An acute angle is smaller than the corner of your folded paper. The tip of a sharpened pencil . The two points of an open pair of compasses . A slightly open pair of scissors . The sharp corner of a set square (the 30° or 45° corner). The clock hands at 1 o’clock . The point of an arrow drawn on the board, and the letter V . Sample answer: the tip of my pencil, the open compasses, the letter V on the board, and the clock at 1 o’clock. Why it happens: When two lines open only a little, the angle between them stays smaller than a right angle, and we call it acute.

Obtuse angles are more than a right angle. Name some objects from your classroom which have an obtuse angle. ________________________________________________________. acute angle obtuse angle The two angles drawn in the book. The dotted arm shows where a right angle would be.

An obtuse angle is wider than the corner of your folded paper. A door opened wide against the wall. A book opened out flat on the desk. The top of a clothes hanger . The clock hands at 4 o’clock . The letter Y , and the roof of a house drawn on the board. A fan blade and the next blade beside it. Sample answer: the wide open door, an open book lying flat, the top of a hanger, and the clock at 4 o’clock. Why it happens: When two lines open past the corner of a square but have not yet become a straight line, the angle is bigger than a right angle, and we call it obtuse.

Identify all angles in the following letters. V A Z The three letters printed in the book: V, A and Z.

Look at every point where two strokes of the letter meet. Letter How many angles What kind V 1 acute — the two strokes meet in a narrow point at the bottom A 5 the top point is acute; where the bar meets each leg there is one acute angle above and one obtuse angle below, so 2 acute + 2 obtuse Z 2 both acute — one where the top bar meets the slanting stroke, one where the slanting stroke meets the bottom bar V A Z The same letters with every angle ringed — red for acute and blue for obtuse. Why it happens: Wherever two strokes meet they make an angle. In the letter A the bar crosses both legs, so each crossing gives two angles — a narrow one above and a wide one below.

NCERT Solutions for Class 4th Maths Chapter 1 Let Us Do — Acute and Obtuse Angles

Book page 12 Updated on2026-09-19

Q1.

Draw some right angles on the dot grid.

A dot grid like the one in the book.

Answer

On a dot grid a right angle is easy: one arm goes across and the other goes straight down or straight up.

Choose a dot. This will be the corner of your angle.
Draw a line to the right, dot to dot.
From the same corner draw a line straight up, dot to dot.
The angle between them is a right angle. Check it with your paper checker.

You can also make a right angle by sloping both arms equally — one going up 2 and across 2, the other going down 2 and across 2.

Sample answer: draw the four corners of a square on the grid; each corner is a right angle, so one square gives you 4 right angles.

Why it happens: The dots are set out in straight rows and straight columns, and a row meets a column at a right angle.

Q2.

Acute angles are less than a right angle. Name some objects from your classroom which have an acute angle. ________________________________________________________.

The two angles drawn in the book. The dotted arm shows where a right angle would be.

Answer

An acute angle is smaller than the corner of your folded paper.

The tip of a sharpened pencil.
The two points of an open pair of compasses.
A slightly open pair of scissors.
The sharp corner of a set square (the 30° or 45° corner).
The clock hands at 1 o’clock.
The point of an arrow drawn on the board, and the letter V.

Sample answer: the tip of my pencil, the open compasses, the letter V on the board, and the clock at 1 o’clock.

Why it happens: When two lines open only a little, the angle between them stays smaller than a right angle, and we call it acute.

Q3.

Obtuse angles are more than a right angle. Name some objects from your classroom which have an obtuse angle. ________________________________________________________.

The two angles drawn in the book. The dotted arm shows where a right angle would be.

Answer

An obtuse angle is wider than the corner of your folded paper.

A door opened wide against the wall.
A book opened out flat on the desk.
The top of a clothes hanger.
The clock hands at 4 o’clock.
The letter Y, and the roof of a house drawn on the board.
A fan blade and the next blade beside it.

Sample answer: the wide open door, an open book lying flat, the top of a hanger, and the clock at 4 o’clock.

Why it happens: When two lines open past the corner of a square but have not yet become a straight line, the angle is bigger than a right angle, and we call it obtuse.

Q4.

Identify all angles in the following letters.

The three letters printed in the book: V, A and Z.

Answer

Look at every point where two strokes of the letter meet.

Letter	How many angles	What kind
V	1	acute — the two strokes meet in a narrow point at the bottom
A	5	the top point is acute; where the bar meets each leg there is one acute angle above and one obtuse angle below, so 2 acute + 2 obtuse
Z	2	both acute — one where the top bar meets the slanting stroke, one where the slanting stroke meets the bottom bar

The same letters with every angle ringed — red for acute and blue for obtuse.

Why it happens: Wherever two strokes meet they make an angle. In the letter A the bar crosses both legs, so each crossing gives two angles — a narrow one above and a wide one below.

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