Why is arctan1 / 2-arctan (- 2) equal to 90 degrees, and how to calculate it?

Why is arctan1 / 2-arctan (- 2) equal to 90 degrees, and how to calculate it?

Let a = arctan1 / 2, B = arctan-2; Tana = 1 / 2, tanb = - 2. Tana * tanb = - 1; so Tana = - cotb = cot (- b) = Tan (90 + b); so a = 90 degrees + B; a + B = 90 degrees
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Arctan (1 / 2)? How much is it? Thank you

26.565
How to calculate arctan 1 / 2 with scientific calculator on Windows
zero point five
Inv
tan

What is arctan √ 3
How do you calculate it

tanπ/3=√3
So arctan √ 3 = π / 3

How much are arctan + infinity and arctan infinity?
By the way, what are arcsin + infinity and arcsin infinity and arccos + infinity and arccos infinity?

The domains of arcsin and arccos are (- 1,1)
So your + inf or - inf is meaningless
in addition
arctan(+inf) = pi/2
arctan(-inf) = -pi/2
arccot(+inf) = 0
arccot(-inf) = pi