Post on 13-Jul-2015
The Rules of Sine
A
B C
c b
a
How about for scalene triangle ?
C
A B
a
c
b
D
h
Height line is the line from an angle of triangle that is perpendicular with opposite side.
Look at the triangle beside!
By the same way, we get :
So, we get :
It is called by the rule of sine.
This rules can be used for cases :
• Two angles and any one side length are given
• Two sides and an angle of opposite side are given
A B
C
a b
c D
Example Determine the size of angle and the length of sides that are not given from the triangle below :
A C
B
5 cm
Answer
Activities Class
1. Determine the undetermined elements from triangle of KLM :
M
K 25 cm L
Given : the angle of K is 400 and the angle of L is 550.
2. Desi and Vita are standing on the edge of a river and are separated as far as 40 m. across the river, Ardi is seen to be standing and looking at both the girls. If the angle formed by Ardi-Desi-Vita is 650 and the angle formed by Ardi-Vita-Desi is 500. Determine the distance of Ardi and Desi and the distance of Ardi from Vita!