Let's say I have cos(5pi/3). How do I know this equals 0.5 without using a calculator?
but if you draw your self that angle ... you'll realize that angle of is the same as the angle of and you know that angle that is
because cos is positive in first and 4th quadrant get it ?
when drawn circle, draw and add it 5 times and you'll see that is the angle
P.S. you realize that so is just for the smaller than so it have to be
Hence, if you draw a unit-circle centred at the origin, you can draw a right-angled triangle
with hypotenuse going off at 60 degrees to the x-axis,
since Cos(angle) gives the x co-ordinate, and Cos(-A)=CosA.
This allows us to draw a regular hexagon, made of equilateral triangles as shown in the attachment.
From that, we can see that