侧面积A=a=y x=√5cost L: y=3sin(0≤t≤) A=|3sint·√5sin2t+9cos2tlt 0 3√5+4cos2 t sin tdt =J5+2dm=9+;n5侧面积   = = L L A zds yds(0 ) 3sin 5cos :       = = t y t x t L  =  +  0 2 2 A 3sin t 5sin t 9cos tdt  = +  0 2 3 5 4cos tsin tdt  = + 2 0 2 3 5 u du ln5 4 15 = 9 +