已知随机变量<img src="https://zk.995w.com/lqwvjeImg/e3/e3fcd460164b6f59370a7df8fe126729.png" style="width:18px;height:16px;" >的概率密度为<img src="https://zk.995w.com/lqwvjeImg/48/4884d3c2b6c590ade5f43940bcbe26fe.png" style="font-size: 20px;" >,则<img src="https://zk.995w.com/lqwvjeImg/e3/e3fcd460164b6f59370a7df8fe126729.png" style="font-size: 0.85rem; width: 18px; height: 16px;" >的期望<img src="https://zk.995w.com/lqwvjeImg/c4/c4dcb11929713228bee96bfbfcd01342.png" style="font-size: 0.85rem; width: 56px; height: 26px;" >( )<br>· <img src="https://zk.995w.com/lqwvjeImg/45/451c87c8ce840681a66cda8837c4e451.png" <br>· <img src="https://zk.995w.com/lqwvjeImg/5b/5b4e597c18fa17ef5271681378375279.png" <br>· <img src="https://zk.995w.com/lqwvjeImg/73/73497d50977469b0b4f92ee9741a2da3.png" <br>·<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/169847431809069e0983a9a8140a7af043c3d0915202aimage82.png"