例5求「,,b a+x 解Ja+x=a2 arctan -+C 1例5 求 . 1 2 2 dx a x  + 解 dx a x  + 2 2 1 dx 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 = +