设二维连续型随机变量(X，Y)服从区域D上的均匀分布，其中 D=(x

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问题问答题

设二维连续型随机变量(X，Y)服从区域D上的均匀分布，其中
D=(x，y)|0≤y≤x≤2-y
试求：

X的边缘概率密度；

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问答题计算题

列车采用韶山3型电力机车牵引，机车质量P=138t，列车牵引质量G=2620t；车辆均采用滚动轴承；计算当列车以最低计算速度运行时，列车基本阻力与列车平均单位基本阻力？