Page 7 - Dahlia Oktaviani Ginting Buku

I and 60 0 angle I

0
30
b.
Look at the following triangle

B
c 0
60 a
0
A 30 b C
D

 ABD equilateral so that every angle 60 . Point C is in
0
the middle of BC, so it is a right triangle ( ACB = 90 0
=
0
). Large BAC = 30 , so long BC = 1 BD and c 2 .
a
2


In ABC applying the Pythagorean theorem:
c = a + b
2
2
2
2
2
( 2a) 2 = a + b
4a = a + b
2
2
2
b = 3a
2
2
b = 3a = a 3
2
The trigonometric ratios for the angles 30 and 60 are:
0
0

a a
0
sin 30 = = = and
1
c 2a 2
b a 3
0
sin 60 = = = 1 3
c 2a 2
I I
0
cos 30 = b = a 2a 3 = 1 2 3
c