【单选题】纯交换经济中,两个人的无差异曲线的切点组成的曲线是( )。
【判断题】第一心音标志心室收缩开始,心室收缩力增强则第一心音加强。
【单选题】It was in the small house was built with stones by his father he spent his childhood.
【单选题】It was in the small house was destroyed by the flood he spent his childhood.
【简答题】直线y=2x-6与x轴交点坐标为______.
【简答题】在直角坐标系中,画出下列向量: (1) | a |=2 , a 的方向与x轴正方向的夹角为60°,与y轴正方向的夹角为30°; (2) | a |=4 , a 的方向与x轴正方向的夹角为30°,与y轴正方向的夹角为120°; (3) | a |=4 2 , a 的方向与x轴正方向的夹角为135°,与y轴正方向的夹角为135°.
【简答题】直线y=3x-6与x轴的交点坐标为______.