dx/dt=-a*sint,dy/dt=b*cost,ds=√((dx/dt)^2+(dy/dt)^2)dt=√(a^2*sint^2+b^2*cost^2)dt其质量=∫ρds=4∫(0,π/2)b*sint*√(a^2*sint^2+b^2*cost^2)dt=4∫(0,π/2)b*sint*√(a^2-（a^2-b^2）*cost^2)dt=4∫(0,π/2...