题目应该是f(x+2)=f(x)吧.
令t=x+2,则f(t)=f(t-2);考虑f(x)=-f(-x),有
f(7.5)=f(5.5)=f(3.5)=f(1.5)=-f(-1.5)=-f(0.5)=-0.5
Good luck!