Originally Posted by

**wiseguy** "Sine is an odd function because when A in sin(A)=y becomes

negative, y becomes negative.

*******Not only is it negative, it's the negative of sin(A).

You need to understand that if sin(A)=k, then sin(-A)=-k.

For example... $\displaystyle sin\left(30^o\right)=0.5\ and\ sin\left(-30^o\right)=-0.5$***************

In a unit circle, the y-coordinate of a point is always

denoted by sinθ. *****the unit-circle is centred at the origin (0,0)*****

Sin(A) equals -sin(-A) because as A crosses below the x axis, sin(-A) equals a negative value.

*****the exact negative of sin(A), if ... $\displaystyle 0<A<180^o$********

Thus, adding a negative sign to sin(-A) creates a positive, rendering it equal to sin(A)."

****the last line is not so important because you can also have angles > 180 degrees*******

I'm going to fly with this. How does it look?