how do I enter a formula to work out tangents

[Simon Peachey]

I am trying to set up a speadsheet in exel to work out the angle of a
triangle, how can i input the formula to work out the Inv Tangent?

 

[Smallweed]

click on Fx (Insert, Function) and choose Math & Trig category - loads of
worksheet functions for this kind of thing, including ATAN

 

[Tom Ogilvy]

ATAN

from help:
Returns the arctangent, or inverse tangent, of a number. The arctangent is
the angle whose tangent is number. The returned angle is given in radians in
the range -pi/2 to pi/2.