令x/2 = u,x = 2u,dx = 2du
∫ f(x/2) dx
= ∫ f(u) · 2du
= 2∫ e^(2u) du
= ∫ e^(2u) d(2u)
= e^(2u) + C
= e^(2 · x/2) + C
= e^x + C