设X,Y是两个随机变量，它们的联合概率密度为<br /> <img src="https://nimg.ppkao.com/2019-04/wuacheng/2019041416143149671.jpg?sign=96ee6e29a71a35a53f45fd021bba8947&t=62d5bff8" /><br /> （1）求（X，Y）关于X的边缘概率密度<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019041416145596495.jpg?sign=c1cba4556065c7b22eb2f29e93ff8536&t=62d5bff8" /><br /> （2）求条件概率密度<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019041416151540744.jpg?sign=16196ddff13c6790582a27ceaf265638&t=62d5bff8" />，写出当x=0.5时的条件概率密度；<br /> （3）求条件概率<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019041416153794203.jpg?sign=dd7317995c51d69a0324bff3d61c2ff0&t=62d5bff8" />