# arc tangent

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## arc tangent

[¦ärk ′tan·jənt]
(mathematics)
Also known as antitangent; inverse tangent.
For a number x, any angle whose tangent equals x.
For a number x, the angle between -π/2 radians and π/2 radians whose tangent equals x ; it is the value at x of the inverse of the restriction of the tangent function to the interval between -π/2 and π/2.
References in periodicals archive ?
[f.sub.az1] = [2[f.sup.a0]/[pi]] arctan [square root of (-[B.sub.z] - [square root of ([B.sup.2.sub.z] - 4[A.sub.z][C.sub.z]/2[A.sub.z])])] (6a)
[phi]' = arctan (r sin [[theta].sub.n,m]/ r cos [[theta].sub.n,m] cos [[phi].sub.n,m] + (n- 1)[DELTA]).
[psi] = -[[k.sup.2.sub.t]z/2k[(1 + [(z/[z.sub.R]).sup.2]] - arctan (z/[z.sub.R]).
[[beta].sub.C, i] = arctan ([d.sub.i] + [R.sub.cell]/[H.sub.HAPS]) for i = 2, ...
Let [theta] = arctan x/z [member of] (-[pi], [pi]] denote the angle, measured parallel to the y = 0 plane, that a point (x, y, z) makes with the positive z-axis (as described in Section 4).
We also need the real elementary functions arcsin, arccos, arctan, log, and log1p, where log1p(x) = log(1 + x).
G = [square root of ([G.sup.2.sub.x] + [G.sup.2.sub.y])] and [theta] = arctan ([G.sub.y]/[G.sub.x]) (4)
[phi] = arctan [cot ([k.sub.h]x) x tanh([k.sub.h]y)] - arctan[cot[[k.sub.h] (x + 2[h.sub.2])) x tanh([k.sub.h]y)], (9)
[theta] = arctan [K.sub.II]/[square root of [K.sup.2.sub.I] + 8 [K.sup.2.sub.II]] - arctan 3 [K.sub.II]/[K.sub.I] (2)
where [[phi].sub.1] = arctan ([u.sub.4]/ [[tau]'.sub.10]) and [[phi].sub.2] = arctan(([[omega]'.sup.2.sub.10] - [u.sub.12][u.sub.4])/ [[omega]'.sub.10]([u.sub.4] + [u.sub.12])).
(4.1) arctan (1/s) = 1/s + [1.sup.2]/3s + [2.sup.2]/5s + [3.sup.2]/7s + [4.sup.2]/9s + ...

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