A circle has radius x cm. What is the area of a sector of the circle with angle 135°, leaving the answer in terms of x and π?
- \( \frac{\pi x^2}{8} \)
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\( \frac{3\pi x^2}{8} \)
- \( \frac{5\pi x^2}{8} \)
- \( \frac{3\pi x}{8} \)