设随机变量X，Y相互独立，它们的联合概率密度为<br /> <img src="https://nimg.ppkao.com/2019-04/wuacheng/2019041416480439408.jpg?sign=ca2abc397fe0a2fcd8cc8501911d3b71&t=62d73ba0" /><br /> （1）求边缘概率密度<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019041416482170176.jpg?sign=f9d081db2330a51c848e785841d15b38&t=62d73ba0" /><br /> （2）求<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019041416484144386.jpg?sign=7cca918e8151e70fe79496aa923e5077&t=62d73ba0" />的分布函数。<br /> （3）求概率<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019041416490035700.jpg?sign=9498aab47c11179d594c7c3b0adc8c8e&t=62d73ba0" />