计算：arctan1/2-arctan(-2)要计算过程.

网友回答

令a=arctan1/2∈(0,π/2)
b=arctan(-2) ∈(-π/2,0)
tana=1/2
tanb=-2
tanatanb=-1
a-b∈(0,π)
cot(a-b)=(1+tanatanb)/(tana-tanb)
=(1-1)/(1/2+2)
=0arctan1/2-arctan(-2) = a-b=π/2.