⑩天掌 Teaching Plan on Advanced Mathematics 功元素为dwp=88.2兀.x.bkx, w=88.2π·x·dx 2 88.2π x2 ≈3462(千焦)Tianjin Polytechnic University Teaching Plan on Advanced Mathematics 功元素为 dw = 88.2 x  dx, w =  x  dx  88.2 5 0 5 0 2 2 88.2       =  x  3462 (千焦)．