f(x) = (ax+b) / (x²+1) ,定义在(-1,1)上的奇函数
f(x) + f(-x) = 0
(ax+b) / (x²+1) + (-ax+b) / (x²+1) = 0
解得b=0,f(x) = ax / (x²+1)
f(t-1)+f(t)