#### hioyo

##### Advanced Member level 4

In chapter 9 the below trigonometric identity is given.

As per my knowledge sin is positive in the 2nd quadrant and negative in all other quadrants(ALL SILVER TEA CUPS). In the first equation

**Sin(wt±180)**means it is lying in the 2nd quadrant and 3rd quadrant depending phase shift is +180 or -180.

When it is lying in the 2nd quadrant**(Sin(wt-180))**it should be positive and when it is lying in the 3rd quadrant **(Sin(wt+180))**should be negative.This is my understanding.

But in the book it is given as

**Sin(wt±180)=-sinwt**.May I know where I went wrong