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题目 已知椭圆x2/9+y2/9=1的焦点为F1、 F2,点P为其上的动点,当∠F1PF2为钝角时, 求点P横坐标的取值范围．
Title It is known that the focus of the ellipse x2/9+y2/9=1 is F1 and F2. The point P is the moving point on it. When ∠F1PF2 is an obtuse angle, the range of the P abscissa is calculated.