f(-x)=-x*sin(-x)=xsinx=f(x)
所以是偶函数
所以f(-π/4)=f(π/4)
因为π/2>π/3>1>π/4>0
sin在第一象限是增函数
所以sin(π/3)>sin1>sin(π/4)>0
π/3>1>π/4>0
所以π/3*sin(π/3)>1*sin1>π/4*sin(π/4)>0
即f(π/3)>f(1)>f(-π/4)