Maths Form 2

Use a equilateral triangle ABC with each side = 2 units. Each angle is 60 degrees.

Draw a perpendicular line from A to BC at D. You will get a right angle triangle ABD with right angle at D, AB=2 units, BD=1 unit, angle B=60 degrees.

Using Pythagoras's Theorem, you can calculate the length of AD:
AD=square root of 2^2 - 1^2 =√3

Therefore,
sin B = AD / AB
sin 60 = √3/2

你可以用對數表求證sin60=√3/2
首先, 從對數表查到sin60=0.866
跟着解√3/2 , 從對數表查到√3=1.7321, 所以√3/2 = 1.7321 / 2 = 0.866
因此, sin60=√3/2