1. 設x與y均為實數,則|x-y| = |x| + |y|成立的充分必要條件是: (A) xy ≥0 (B) xy ≤0 (C) xy>0 (D) xy<0

8. 若x siny=y sinx,則 \( \frac{dy}{dx} \)是:(A)\( \frac{2x \sin y + y^2 \cos x}{2y \sin x + x^2 \cos y} \)(B) \( \frac{2x \sin y - y^2 \cos x}{2y \sin x + x^2 \cos y} \)(C)\( \frac{2x \sin y + y^2 \cos x}{2y \sin x - x^2 \cos y} \)(D)\( \frac{2x \sin y - y^2 \cos x}{2y \sin x - x^2 \cos y} \)