第7章 7.11

(1)

$dy = 3x^2 dx$

(2)

$dy = \frac{1}{2\sqrt{x+1}} dx$

(3)

$dy = \frac{-2t}{(t^2+1)^2} dt$

(4)

$dy = \frac{1}{\cos^2 x} dx$

(5)

$dy = \frac{2x}{x^2+1} dx$

(6)

$dy = e^x dx$