The Arccos (cos^-1) command

Command Summary

Takes the inverse cosine of a number (usually, an integer or fraction).

Command Syntax

cos^-1(angle)

Menu Location

Press [2nd] COS button to enter cos^-1(.

Calculator Compatibility

This command works on all calculators.

Token Size

1 byte

The cos^-1() command returns the inverse cosine of an angle measure. Naturally, the result depends on the angle mode the calculator is in: radian, degree, or (in AMS version 3.10) gradian. You can also use one of the ^r, °, ^G marks to specify an angle mode.

For many common angles, cos^-1() can compute an exact result. Other angles, the calculator will leave alone unless it's in approximate mode (or unless you make it approximate), and then it will give a decimal approximation. As long as the calculator is in radian mode, cos^-1() can be used with complex numbers as well.

:cos⁻¹(1/2)
           π/3
:cos⁻¹(-1/2)
           2π/3
:cos(cos⁻¹(x))
           x

If cos^-1() is applied to a list, it will take the inverse cosine of every element in the list.

Advanced Uses

The cos^-1() of a matrix is not (in general) the same as taking the cosine of every element of the matrix. I hope that someone more qualified to talk about this updates this part of the page.

Error Conditions

• Please update this part too

Related Commands

• sin()
• tan()
• cos()