[tex] \text{tg}\Big(\dfrac{\pi}{2} - \text{arctg}\Big(\dfrac{1}{2} \Big)\Big) = \text{ctg}}\Big(\text{arctg}\Big(\dfrac{1}{2} \Big)\Big) = \\ \\ \boxed{\text{Am folosit formula: } \text{tg}\Big(\frac{\pi}{2} -x\Big) = \text{ctg}(x)} \\ \\ = \dfrac{1}{\dfrac{1}{2}} = 2\\ \\ \boxed{\text{Am folosit formula: } \text{ctg}(\text{arctg}\,x) = \dfrac{1}{x}} [/tex]