=( 1/4)∫ 1/( 1+(4x)？ )d(4x)

=( 1/4) arctangent (4x)+C

14、f '(x)=3x？ -6x-9=3(x？ -2x-3)=3(x-3)(x+ 1)

Stationary point: x=3, x=- 1.

f ''(x)=6x-6

f ' '(3)= 12 & gt； 0, so x=3 is the minimum point, and f(3)=-27.

f ''(- 1)=- 12