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arc tangent[¦ärk ′tan·jənt]
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.