Class 9 Maths – Triangles MCQ

1. Which of the following cannot represent the sides of a triangle?

a) 3 cm, 4 cm, 7 cm
b) 5 cm, 12 cm, 13 cm
c) 6 cm, 8 cm, 10 cm
d) 7 cm, 24 cm, 25 cm

Answer:

a) 3 cm, 4 cm, 7 cm

Explanation:

The sum of the lengths of any two sides of a triangle must be greater than the third side. 3 + 4 = 7 which is not greater than the third side.

2. In an equilateral triangle, each angle measures:

a) 45°
b) 60°
c) 90°
d) 120°

Answer:

b) 60°

Explanation:

An equilateral triangle has all three sides equal, and all its angles measure 60°.

3. The triangle with one angle measuring more than 90° is called:

a) Acute-angled triangle
b) Equilateral triangle
c) Obtuse-angled triangle
d) Right-angled triangle

Answer:

c) Obtuse-angled triangle

Explanation:

A triangle with one angle greater than 90° but less than 180° is termed as an obtuse-angled triangle.

4. The Pythagoras theorem is applicable to:

a) Equilateral triangle
b) Acute-angled triangle
c) Obtuse-angled triangle
d) Right-angled triangle

Answer:

d) Right-angled triangle

Explanation:

Pythagoras theorem (a^2 + b^2 = c^2) is valid for a right-angled triangle where 'c' is the hypotenuse.

5. If the sides of a triangle are 15 cm, 15 cm, and 15 cm, then the triangle is:

a) Isosceles
b) Scalene
c) Equilateral
d) Right-angled

Answer:

c) Equilateral

Explanation:

An equilateral triangle has all its sides of the same length.

6. If two angles of one triangle are equal to two angles of another triangle, then both triangles are:

a) Similar
b) Congruent
c) Equilateral
d) Isosceles

Answer:

a) Similar

Explanation:

Triangles with corresponding angles equal are similar.

7. If the sides of a triangle are in the ratio 3:4:5, the triangle is:

a) Acute-angled
b) Right-angled
c) Obtuse-angled
d) Equilateral

Answer:

b) Right-angled

Explanation:

A triangle with sides in the ratio 3:4:5 is a Pythagorean triplet and represents a right-angled triangle.

8. In a triangle ABC, if AB = AC, then:

a) ∠B = ∠C
b) ∠B > ∠C
c) ∠B < ∠C
d) ∠B ≠ ∠C

Answer:

a) ∠B = ∠C

Explanation:

In an isosceles triangle, angles opposite to equal sides are equal.

9. The sum of all the angles of a triangle is:

a) 90°
b) 180°
c) 270°
d) 360°

Answer:

b) 180°

Explanation:

The sum of all interior angles of a triangle is always 180°.

10. A triangle with all its angles less than 90° is called:

a) Right-angled triangle
b) Obtuse-angled triangle
c) Acute-angled triangle
d) Equilateral triangle

Answer:

c) Acute-angled triangle

Explanation:

An acute-angled triangle has all its angles less than 90°.

11. The perimeter of a triangle is:

a) The sum of its sides
b) Half the sum of its sides
c) Twice the sum of its sides
d) The product of its sides

Answer:

a) The sum of its sides

Explanation:

The perimeter of any polygon, including a triangle, is the sum of its sides.

12. In a right-angled triangle, the side opposite the right angle is called:

a) Adjacent
b) Opposite
c) Hypotenuse
d) Base

Answer:

c) Hypotenuse

Explanation:

The side opposite the right angle in a right-angled triangle is the longest side and is called the hypotenuse.

13. If two sides of a triangle are equal, then it is called:

a) Equilateral triangle
b) Isosceles triangle
c) Scalene triangle
d) Right-angled triangle

Answer:

b) Isosceles triangle

Explanation:

An isosceles triangle has two sides of equal length.

14. Which of the following can be the sides of a right-angled triangle?

a) 6 cm, 8 cm, 10 cm
b) 7 cm, 24 cm, 26 cm
c) 5 cm, 10 cm, 15 cm
d) 4 cm, 5 cm, 7 cm

Answer:

a) 6 cm, 8 cm, 10 cm

Explanation:

Using Pythagoras theorem, only the set of sides 6 cm, 8 cm, and 10 cm satisfy the condition a^2 + b^2 = c^2.

15. An exterior angle of a triangle is equal to:

a) Sum of the opposite interior angles
b) Difference of the opposite interior angles
c) Half the sum of the opposite interior angles
d) Twice the sum of the opposite interior angles

Answer:

a) Sum of the opposite interior angles

Explanation:

The measure of an exterior angle of a triangle is equal to the sum of the measures of the two non-adjacent interior angles.

16. If a triangle has sides of lengths 4 cm, 5 cm, and 7 cm, it is:

a) Equilateral
b) Isosceles
c) Scalene
d) Right-angled

Answer:

c) Scalene

Explanation:

A scalene triangle has all sides of different lengths.

17. The area of a triangle with base 'b' and height 'h' is:

a) b*h
b) b*h/2
c) 2*b*h
d) b^2*h

Answer:

b) b*h/2

Explanation:

The area of a triangle is given by (base x height)/2.

18. The triangle with sides 5 cm, 12 cm, and 13 cm is:

a) Acute-angled
b) Right-angled
c) Obtuse-angled
d) Equilateral

Answer:

b) Right-angled

Explanation:

The sides 5 cm, 12 cm, and 13 cm form a Pythagorean triplet, which is characteristic of a right-angled triangle.

19. Which of the following is not a property of an equilateral triangle?

a) All sides are equal
b) All angles are 60°
c) It has one angle of 90°
d) The altitudes bisect the base

Answer:

c) It has one angle of 90°

Explanation:

An equilateral triangle has all its angles measuring 60°.

20. The triangle which has no equal sides and no equal angles is:

a) Equilateral
b) Isosceles
c) Scalene
d) Right-angled

Answer:

c) Scalene

Explanation:

A scalene triangle has all its sides and angles of different measures.

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