## Trigonometry (10th Edition)

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