Class 9 Maths – Heron’s Formula MCQ

1. Heron's formula is used to find the area of a triangle given:

a) Its height and base
b) The three angles
c) The three side lengths
d) Its altitude and median

Answer:

c) The three side lengths

Explanation:

Heron's formula calculates the area of a triangle when all three side lengths are known.

2. If a triangle has sides of length a, b, and c, the semi-perimeter (s) is calculated as:

a) s = a + b + c
b) s = (a + b + c) / 2
c) s = 2(a + b + c)
d) s = a + b

Answer:

b) s = (a + b + c) / 2

Explanation:

The semi-perimeter is half the total perimeter of the triangle.

3. According to Heron's formula, the area (A) of a triangle with side lengths a, b, and c, and semi-perimeter s is:

a) A = sqrt(s(a + b + c))
b) A = s(a + b + c)
c) A = sqrt(s(s – a)(s – b)(s – c))
d) A = 2s(s – a)(s – b)(s – c)

Answer:

c) A = sqrt(s(s – a)(s – b)(s – c))

Explanation:

Heron's formula expresses the area in terms of the semi-perimeter and the side lengths.

4. For a triangle with sides 5 cm, 12 cm, and 13 cm, its semi-perimeter is:

a) 15 cm
b) 30 cm
c) 7.5 cm
d) 5 cm

Answer:

a) 15 cm

Explanation:

Semi-perimeter, s = (5 + 12 + 13) / 2 = 30 / 2 = 15 cm.

5. If the three sides of a triangle are equal in length, the triangle is:

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

Answer:

c) Equilateral

Explanation:

A triangle with all three sides of equal length is an equilateral triangle.

6. Heron's formula can be applied to which of the following triangles?

a) Only equilateral triangles
b) Only isosceles triangles
c) Only right-angled triangles
d) Any triangle with known side lengths

Answer:

d) Any triangle with known side lengths

Explanation:

Heron's formula is applicable for any triangle as long as the side lengths are known.

7. If one side of a triangle is longer than the sum of the other two sides, the area of the triangle is:

a) Zero
b) Infinite
c) Negative
d) Undefined

Answer:

d) Undefined

Explanation:

If one side is longer than the sum of the other two, the triangle cannot exist, making its area undefined.

8. The expression "s(s – a)(s – b)(s – c)" is often seen in:

a) Pythagoras' theorem
b) Area of a rectangle formula
c) Area of a circle formula
d) Heron's formula for the area of a triangle

Answer:

d) Heron's formula for the area of a triangle

Explanation:

This expression forms the core of Heron's formula for calculating the area of a triangle.

9. In Heron's formula, if s is the semi-perimeter, then the perimeter of the triangle is:

a) s / 2
b) s
c) 2s
d) s^2

Answer:

c) 2s

Explanation:

Since s is half the perimeter, the full perimeter would be 2s.

10. If a triangle has an area of zero according to Heron's formula, then:

a) The triangle doesn't exist
b) All sides of the triangle are equal
c) The triangle is a right triangle
d) The triangle is an acute triangle

Answer:

a) The triangle doesn't exist

Explanation:

If the area is zero, it implies that the three points are collinear, and thus, it's not a valid triangle.

11. The value of s(s – a)(s – b)(s – c) must be:

a) Positive
b) Zero
c) Negative
d) Can be positive or negative

Answer:

a) Positive

Explanation:

Since the area of a triangle cannot be negative, the value inside the square root in Heron's formula must be positive.

12. Heron of Alexandria is also known for:

a) His work on number theory
b) His work on calculus
c) His steam engine
d) His work on trigonometry

Answer:

c) His steam engine

Explanation:

Heron is also known for creating the first recorded steam engine, called an aeolipile.

13. For a triangle with sides 6 cm, 8 cm, and 10 cm, its area using Heron's formula is:

a) 24 cm^2
b) 48 cm^2
c) 30 cm^2
d) 36 cm^2

Answer:

a) 24 cm^2

Explanation:

Using Heron's formula, we find the semi-perimeter to be 12 cm and the area to be 24 cm^2.

14. A triangle with sides a, b, and c can have an area greater than zero if:

a) a + b > c, b + c > a, and c + a > b
b) a + b < c, b + c < a, and c + a < b
c) a = b = c
d) a^2 = b^2 + c^2

Answer:

a) a + b > c, b + c > a, and c + a > b

Explanation:

For a triangle to exist, the sum of the lengths of any two sides must be greater than the length of the third side.

15. If a triangle is isosceles with sides a, a, and b, then its area using Heron's formula is:

a) sqrt(s(s – a)(s – a)(s – b))
b) sqrt(s(a^2 – b^2))
c) a^2 sqrt(s – b)
d) b^2 sqrt(s – a)

Answer:

a) sqrt(s(s – a)(s – a)(s – b))

Explanation:

For an isosceles triangle using Heron's formula, the formula simplifies as given in option a.

16. The main advantage of Heron's formula over the ½ × base × height formula is:

a) It's more accurate
b) It can be used even when the height is not known
c) It's easier to memorize
d) It's more versatile for different shapes

Answer:

b) It can be used even when the height is not known

Explanation:

Heron's formula comes in handy especially when the triangle's height isn't available.

17. Heron's formula can be derived from:

a) Pythagoras' theorem
b) Trigonometry identities
c) Area of parallelogram formula
d) Binomial theorem

Answer:

a) Pythagoras' theorem

Explanation:

Heron's formula can be derived using the Pythagoras' theorem for right triangles.

18. If in Heron's formula, s is the semi-perimeter and A is the area, then for a triangle with sides a, b, and c:

a) A = s
b) A > s
c) A < s
d) A can be equal to, less than, or greater than s

Answer:

c) A < s

Explanation:

Generally, the area of a triangle is smaller than its semi-perimeter.

19. The dimensions that make the value inside the square root of Heron's formula negative, result in:

a) An acute triangle
b) A right triangle
c) An obtuse triangle
d) An impossible triangle

Answer:

d) An impossible triangle

Explanation:

A negative value inside the square root means the triangle doesn't satisfy the triangle inequality theorem and hence, cannot exist.

20. Heron's formula is especially useful for:

a) Calculating the area of a square
b) Finding the height of a triangle
c) Calculating the area of triangles in coordinate geometry
d) Calculating the side length of a triangle

Answer:

c) Calculating the area of triangles in coordinate geometry

Explanation:

When working in coordinate geometry, often only the side lengths are known making Heron's formula very useful.

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