y=(tanx)^2+3tanx+2,x∈[-π/4,π/2],则其值域为＿令tanx=a,由于x∈[-π/4,π/2],那么a>=-1y=(a)^2+3a+2 a>=-1y=(a)^2+3a+2=(a+2)(a+1)y>=0
