■例1 x x=√x2+1 √5 ■例2 11+x 4 C dx 01+x 6 1+x 2 3J01+x arctan x -arctan x O 3 O 3◼ 例1 ◼ 例2 2 2 2 0 2 0 1 5 1 1 x x dx x x = = + = − +  4 1 1 1 6 2 6 0 0 0 1 1 3 0 0 1 1 1 1 3 1 1 arctan arctan 3 3 x x x dx dx dx x x x x x  = = + = + + + + = + =   