The Arccos (cos^-1) command


Command Summary

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

Command Syntax


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.


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

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