25.将积分化为极坐标形式 R R R Ⅰ=[4+gdxf()dy+」kd f(d 0 √1+R tanr R do f(tanO)rdr arctan r R f(tan )do. rdr r=R 0 0 R 2 tanr ∫(tanb)d 2 arctan R25. 将积分化为极坐标形式 r =R  + R R   + −    + R R R R x y x y x f 2 1 1 2 d ( )d d ( )d   +   R R Rx y x y x f D1 D2 . . R 0 y x D d (tan ) d arctan   R R θ f θ r r (tan )d arctan    = R f θ θ R . . . 2 2 y = R − x (tan )d d arctan   = R R f θ θ r r arctanR I = I =