Trig Reciprocal Quadrant
1. The problem asks for the reciprocal of $\sin\theta$. The reciprocal of a trigonometric function $f(\theta)$ is $\frac{1}{f(\theta)}$. For $\sin\theta$, the reciprocal is $\csc\theta$. So, the answer is $\csc\theta$.
2. Next, we determine the quadrant of angle $\theta$ given $\cos\theta < 0$ and $\sin\theta > 0$. Recall the signs of sine and cosine in each quadrant:
- Quadrant I: $\sin > 0$, $\cos > 0$
- Quadrant II: $\sin > 0$, $\cos < 0$
- Quadrant III: $\sin < 0$, $\cos < 0$
- Quadrant IV: $\sin < 0$, $\cos > 0$
Since $\sin\theta > 0$ and $\cos\theta < 0$, $\theta$ lies in Quadrant II.
3. Given $\tan\theta = -\frac{2}{3}$ and $\sec\theta > 0$, find $\csc\theta$.
Step 1: Recall that $\tan\theta = \frac{\sin\theta}{\cos\theta} = -\frac{2}{3}$.
Step 2: Since $\sec\theta = \frac{1}{\cos\theta} > 0$, $\cos\theta > 0$. Tangent is negative and cosine positive, so $\theta$ is in Quadrant IV.
Step 3: Use the Pythagorean identity:
$$1 + \tan^2\theta = \sec^2\theta$$
Calculate $\sec\theta$:
$$1 + \left(-\frac{2}{3}\right)^2 = \sec^2\theta$$
$$1 + \frac{4}{9} = \sec^2\theta$$
$$\frac{13}{9} = \sec^2\theta$$
$$\sec\theta = \frac{\sqrt{13}}{3}$$ (positive as given)
Step 4: Find $\cos\theta$:
$$\cos\theta = \frac{1}{\sec\theta} = \frac{3}{\sqrt{13}}$$
Step 5: Find $\sin\theta$ using $\tan\theta = \frac{\sin\theta}{\cos\theta}$:
$$-\frac{2}{3} = \frac{\sin\theta}{\frac{3}{\sqrt{13}}}$$
$$\sin\theta = -\frac{2}{3} \times \frac{3}{\sqrt{13}} = -\frac{2}{\sqrt{13}}$$
Step 6: Calculate $\csc\theta = \frac{1}{\sin\theta}$:
$$\csc\theta = \frac{1}{-\frac{2}{\sqrt{13}}} = -\frac{\sqrt{13}}{2}$$
Therefore, the value of $\csc\theta$ is $-\frac{\sqrt{13}}{2}$.