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4.04 Area of a triangle

Worksheet
Area of non-right angle triangles
1

Calculate the area of the following triangles, correct to two decimal places:

a
b
c
d
e
f
g
h
2

Calculate the area of the following triangle. Round your answer to the nearest square centimetre.

3

\triangle ABC has an area of 520\text{ cm}^{2}. The side BC = 48\text{ cm} and \angle ACB = 35 \degree.

Find the length of b to the nearest centimetre.

4

Consider the diagram of an isosceles triangle, with perpendicular height h, and base b:

a

Find an expression for h in terms of \theta and a.

b

Find an expression for b in terms of \theta and a.

c

Use the formula for the area of a triangle, A = \dfrac{1}{2}bh, to form an expression for the area of the larger triangle in terms of \theta and a.

5

Use the sine rule to prove that the area of \triangle ABC is given by the equation: \text{Area} = \frac{a^{2} \sin B \sin C}{2 \sin A}

6

Consider the following parallelogram:

a

Find the area of the triangle formed by the points X, Y and Z, in terms of x, y, and \sin Z.

b

Hence, find the area of the parallelogram in terms of x, y, and \sin Z.

7

Consider the given triangle:

a

Find \angle BAC, to one decimal place.

b

Calculate the area of the triangle, to two decimal places.

8

Consider the given triangle:

a

Find the size of angle x, to the nearest minute.

b

Calculate the area of the triangle, to one decimal place.

9

For the following triangles, calculate the following:

i

The size of angle x, to the nearest degree.

ii

The area of the triangle, to one decimal place.

a
b
c
10

Consider the given triangle:

a

Find the value of the angle x, to the nearest second.

b

Hence or otherwise, find the area of the triangle, to one decimal place.

11

Consider the given triangle:

a

Calculate the size of the largest angle of the triangle. Round your answer to the nearest minute.

b

Calculate the area of the triangle, to two decimal places.

12

Consider a triangle with side lengths of 7 \text{ cm, }9 \text{ cm} and 4\text{ cm} respectively:

a

Find the size of angle x, opposite the side that is 7 \text{ cm} long, to the nearest second.

b

Calculate the area of the triangle, to one decimal place.

13

Consider the triangle shown:

a

Find the length of BC, to two decimal places.

b

Hence or otherwise, find the area of the triangle, to two decimal places.

14

For the triangle shown, find the following, rounded to one decimal place:

a

The length of AC.

b

The area of \triangle ACD.

c

The area of \triangle ABC.

15

An equilateral triangle has an area of 25 \sqrt{3}\text{ cm}^2. Find the length of each side of the triangle.

16

If the area of \triangle ABC is 5600 \text{ cm}^2 with a = 200 \text{ cm} and b = 60 \text{ cm}, find the two possible values for the size of \angle ACB. Round each angle to the nearest minute.

17

A triangle has sides in the ratio 4:13:15 and a perimeter of 96\text{ cm}.

a

If the sides are 4 x, 13 x and 15 x, find the value of x.

b

Find the value of angle \theta, that is opposite the shortest side. Round your answer to the nearest second.

c

Find the area of the triangle, to one decimal place.

18

Consider the following diagram:

Find the area of the shaded triangle in terms of x, \alpha, \beta, \phi, and \theta.

Applications
19

The diagram shows a triangular paddock with measurements as shown:

a

Find the area of the paddock. Round your answer to the nearest square metre.

b

State the area in hectares. Round your answer to two decimal places.

20

An industrial site in the shape of a triangle is to take up the space between where three roads intersect.

Calculate the area of the site, correct to two decimal places.

21

The Bermuda triangle is an area in the Atlantic Ocean where many planes and ships have mysteriously disappeared. Its vertices are at Bermuda, Miami and Puerto Rico.

Find the area taken up by the Bermuda Triangle. Round your answer to the nearest square kilometre.

22

A triangular-shaped field has sides of length 25 \text{ m}, 39 \text{ m} and 40 \text{ m}.

a

Find the size of angle x, opposite the side that is 25\text{ m} long. Round your answer to the nearest second.

b

Hence or otherwise, find the area of the field, to one decimal place.

c

Dave has been hired to plough the field and to erect fencing around its perimeter. If he charges \$2 per square metre for ploughing and \$7 per metre for fencing, find his total charge.

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Outcomes

MA11-1

uses algebraic and graphical techniques to solve, and where appropriate, compare alternative solutions to problems

MA11-3

uses the concepts and techniques of trigonometry in the solution of equations and problems involving geometric shapes

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