f(x)^2=(sinx)^2/（5+4cosx)=-0.25[(cosx)^2-1/(cosx+1.25)]令a=cosx+1.25,所以a属于[0.25,1.25]所以f(x)^2=-0.25[(x-1.25)^2-1/x]=-0.25(x+9/16x-2.5)当且仅当x=0.75时x+9/16x有最小值,此时f(x)^2 max=0.25f(x)^2 m...