令x∈(-1,0)则 -x∈（0,1）,所以 f(-x) = 2^-x/(4^-x+1) = 2^x/(4^x+1)
f(x)为奇函数,所以f(-x) = 2^-x/(4^-x+1) = 2^x/(4^x+1) = -f(x)
f(x) = -2^x/(4^x+1)
x=0时,由于奇函数,所以f(0) = 0
x = 1和x=-1时,由于周期为2所以f(1) = f(-1)另外还是奇函数,所以f(-1) = -f(1) = f(1)
因此f(1) = f(-1) = 0
f(x)在[-1,1]上的解析式就是
-2^x/(4^x+1) x∈(-1,0)
f(x) = 2^x/(4^x+1) x∈(0,1)
0 x = -1,0,1
(2)单调性f(x) = 2^x/(4^x+1) x∈（0,1）令 t = 2^x 则t∈(1,2),且t的对x单调递增
原式化为 f(t) = t/(t^2+1)
学过导数的话可以直接求导了,f'(t) = (t^2+1-2t^2)/(t^2+1)^2 = (1-t^2)/(t^2+1)^2< 0
所以在（0,1）上单调递减
如果没有学过导数,则选t'>t f(t') - f(t) = t'/(t'^2+1) - t/(t^2+1) = ( tt'-1)(t-t')/(t^2+1)(t^2+1)
