Yes, ARCTANGENT is a Scrabble word!

Letter values in Scrabble US: A 1, R 1, C 3, T 1, A 1, N 1, G 2, E 1, N 1, T 1.

Is it a valid word?

ARCTANGENT is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the inverse function of the tangent; the angle that has a tangent equal to a given number

Also: arc tangent, inverse tangent.

Not playable in Scrabble US: ARCTAN.