设对角线长为2a,夹角为θ,则知一边长为2a*sin(θ/2)另一边长为2a*cos(θ/2)则矩形面积S=2a*sin(θ/2)*2a*cos(θ/2)=2a^2*[2sin(θ/2)cos(θ/2)]=2a^2*sinθ又0≤sinθ≤1,当且仅当sinθ=1,θ=90°时有Smax=2a^2此时...