1. **Problem:** Define the ASTC Rule. 2. **Explanation:** The ASTC Rule is a mnemonic to remember the signs of trigonometric functions in the four quadrants of the unit circle. 3. **Rule:** - A (All) means all trigonometric functions are positive in the 1st quadrant. - S (Sine) means only sine and cosecant are positive in the 2nd quadrant. - T (Tangent) means only tangent and cotangent are positive in the 3rd quadrant. - C (Cosine) means only cosine and secant are positive in the 4th quadrant. 4. **Summary:** $$\text{Quadrant 1: All positive}$$ $$\text{Quadrant 2: Sine positive}$$ $$\text{Quadrant 3: Tangent positive}$$ $$\text{Quadrant 4: Cosine positive}$$ This helps in determining the sign of trigonometric functions based on the angle's quadrant. **Final answer:** The ASTC Rule states that All functions are positive in quadrant 1, Sine in quadrant 2, Tangent in quadrant 3, and Cosine in quadrant 4.