# How this is possible? "atan(x) function problem"

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Berat Can Karatas on 11 Oct 2019
Answered: Hemant Verma on 11 Oct 2019
Hello Everyone!
I want to calculate the arctan function in MatLab.
But the result is a situation that I do not understand.
Normally, x = atan (1/0) is compleately NaN
Also, matlab says that x = arctan (1/0)
= 1.5708
How is that possible?

Hemant Verma on 11 Oct 2019
Just recall the basics of trigonometry, for a right-angled triangle
,
where P denotes perpendicular, B denotes base and θ denotes angle between hypotenuse and base of triangle.
In your case, where you want to compute arctan(1/0), the length of base B of triangle becomes 0. As B tends to 0, the hypotenuse and perpendicular of triangle start becoming colinear, and θ tends to 90 degrees or (i.e 1.5708) radians.
That's why you get

Stephan on 11 Oct 2019
Edited: Stephan on 11 Oct 2019
What is the problem?
a = 1/0
a =
Inf
atan(a)
ans =
1.5708
fplot(@(x)atan(x),[-100 100],'-b','LineWidth',2)
looks like the Wiki-Entry for me:

R2019b

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