## Trigonometry (10th Edition)

1.$\cos\theta=\frac{x}{r}$ If cosine is negative, that means x must be negtive (since r is always positive) That can be only II and III quadrants 2.$\tan\theta=\frac{y}{r}$ If tangent is negative, that means y and x must be different signs. That can be only II and IV quadrants 3. For both tangent and cosine to be negative, we must be in Quadrant II