f(x)= -4sinx＾2+4cosx+1-a=4cos^2x +4cosx-3-a令t=cosx,x∈[-π/4,2π/3],得t∈[-1/2,1],所以y=4t^2 +4t-3-a,t∈[-1/2,1],f(x)=0恒有解,则a=4t^2 +4t-3,t∈[-1/2,1]总有意义,由于g(t)=4t^2 +4t-3,t∈[-1/2,1],得g(t...