填空题 <img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20240620/14288044_0.png"><br/> (1)将f(x)展开为x的幂级数；<br/> (2)利用(1)的结果，求数项级数<img border="0" alt="" src="https://tuku.weimei168.com/uploads/upimg/20240620/14288044_0_1.png">的和．