1. **Problem Statement:** Find the related acute angle for the angle 135° in standard position. 2. **Formula and Rules:** The related acute angle is the smallest positive angle between the terminal side of the given angle and the x-axis. For angles in the second quadrant (90° to 180°), the related acute angle is calculated as: $$\text{Related acute angle} = 180^\circ - \theta$$ 3. **Intermediate Work:** Given $\theta = 135^\circ$, which lies in the second quadrant. Calculate: $$180^\circ - 135^\circ = 45^\circ$$ 4. **Explanation:** Since 135° is in the second quadrant, its related acute angle is the difference between 180° and 135°, which is 45°. **Final Answer:** The related acute angle for 135° is $45^\circ$.