Question

Sebuah segitiga ABC, dengan panjang BC = 2 cm, AB = 4 cm, Ð B = 60º. Panjang AC adalah ......... ( Aturan Cosinus )

Answer 1

After translating it into English:

In the question, we have the following information.

AB = 4 cm

BC = 2 cm

Angle at B = 60º

First we have to draw the line AB.

Then make an angle of 60º at point B. Draw a straight line from B to 60º.

Open the compass of 2 cm and draw an arc from point B. It will become BC.

Join A & C.

Kindly see the Attachment.

Answer 2

To solve this problem we have to use the laws of cosine that is the extension of the Pythagoras theorem.

If the triangle is ABC then we have here,  

AC^2= AB^2+BC^2-[2*AB*BC*cos(B)].

Right parenthesis is used here to avoid any problem,

Therefore, we have putting the numbers here,

AC^2= 16+4-[2*4*2(1/2)], AC^2 = 20-8, AC^2=12, AC = sqrt(12)