# Inverse Trigonometric Functions

Arcsine: ASin(x) = ATan2(x, SqRt(1 - Sq(x)), but error if |x| > 1.
See: Inverse Sine -- From MathWorld
and Wolfram Function Evaluation

Arccosine: ACos(x) = ATan2(SqRt(1 - Sq(x), x), but error if |x| > 1.
See: Inverse Cosine -- From MathWorld
and Wolfram Function Evaluation

Arctangent: ATan(x) = x - x^3 / 3 + x^5 / 5 ...
See: Inverse Tangent -- From MathWorld
and Wolfram Function Evaluation

If x = 0 and y = 0, ATan2(0, 0) = 0,
Else if x = 0, y > 0, ATan2(pos, 0) = Pi/2,
Else if x = 0, y < 0, ATan2(neg, 0) = -Pi/2,
Else if x > 0, ATan2(y, pos) = ATan(y/x),
Else if x < 0, y >= 0 ATan2(pos, neg) = ATan(y/x) + Pi,
Else if x < 0, y < 0 ATan2(neg, neg) = ATan(y/x) - Pi.
See: Inverse Tangent -- From MathWorld
and Wolfram Function Evaluation

Arccotangent: ACot(x) = ATan(1/x),
but if x = 0, ACot(0) = +/−Pi/2, +Pi/2 is principal value.
See: Inverse Cotangent -- From MathWorld
and Wolfram Function Evaluation

Arcsecant: ASec(x) = ACos(1/x),
but ASec(0) is not defined.
See: Inverse Secant -- From MathWorld
and Wolfram Function Evaluation

Arccosecant: ACsc(x) = ASin(1/x),
but ACsc(0) is not defined.
See: Inverse Cosecant -- From MathWorld
and Wolfram Function Evaluation

See: Transcendental Function Evaluation