f(x)=f(x+3)
f(9/2)=f(3/2+3)=f(3/2)=f(-3/2+3)=f(-3/2)
即f(3/2)=f(-3/2)
奇函数则f(-3/2)=-f(3/2)
所以f(3/2)=-f(3/2)
所以f(3/2)=0
所以f(9/2)=0
f(x)=f(x+3)
f(9/2)=f(3/2+3)=f(3/2)=f(-3/2+3)=f(-3/2)
即f(3/2)=f(-3/2)
奇函数则f(-3/2)=-f(3/2)
所以f(3/2)=-f(3/2)
所以f(3/2)=0
所以f(9/2)=0