Question

A farmer has a field in the shape of a triangle. The farmer has asked the manufacturing class at your school to build a metal fence for his farm. From one vertex, it is 435 m to the second vertex and 656 m to the third vertex. The angle between the lines of sight to the second and third vertices is 49°. Calculate how much fencing he would need to enclose his entire field.

Answer 1

Fencing required = 1586 m

Explanation:

The given statements can be thought of a triangle
`\triangle ABC` as shown in the diagram attached.

A be the 1st vertex, B be the 2nd vertex and C be the 3rd vertex.

Distance between 1st and 2nd vertex, AB = 435 m

Distance between 2nd and 3rd vertex, AC = 656 m

`\angle A =49^\circ`

To find:

Fencing required for the triangular field.

Solution:

Here, we know two sides of a triangle and the angle between them.

To find the fencing or perimeter of the triangle, we need the third side.

Let us use Cosine Rule to find the third side.

Formula for cosine rule:

`cos A = (b^(2)+c^(2)-a^(2))/(2bc)`

Where

a is the side opposite to
`\angle A`

b is the side opposite to
`\angle B`

c is the side opposite to
`\angle C`

`\Rightarrow cos 49^\circ = (656^(2)+435^(2)-BC^(2))/(2* 435* 656)\\\Rightarrow BC^2 = 430336+189225-2 (435)(656)cos49^\circ\\\Rightarrow BC^2 = 430336+189225-570720* cos49^\circ\\\Rightarrow BC^2 =619561-570720* cos49^\circ\\\Rightarrow BC \approx 495\ m`

Perimeter of the triangle = Sum of three sides = AB + BC + AC

Perimeter of the triangle = 435 + 495 + 656 = 1586 m

Fencing required = 1586 m