例 5 求 十 解 d 十 =arctan+ C例5 求 . 1 2 2 d x a x  + 解 d x a x  + 2 2 1 d x a a x  + = 2 2 2 1 1 1             + =  a x d a a x 2 1 1 1 arctan . 1 C a x a = +