由公式(cos(x/2))^2=(1+cosx)/2 ->cosx=2(cos(x/2))^2-1
所以
∫1/(1+cosx)dx
=∫1/(2(cos(x/2))^2)dx
=∫1/((cos(x/2))^2)d(x/2)
=∫1/((cosa)^2)da (其中a=x/2)
=tanu+C
=tanx/2+C (C为x的常数)
∫1/(1+cosx)dx
=∫1/(2cosx/2^2)dx
=∫1/(cosx/2^2)d(x/2)
=∫1/(cosu^2)du
=tanu+C
=tanx/2+C