Интеграл от 0 до + бесконечности dx/(x^2+4)
=(1/2)arctg(x/2)|^(+∞)_(0)= =(1/2)*lim_(x→+∞)arctg(x/2)-(1/2)*arctg0= =(1/2)*(π/2)-(1/2)*0=π/4