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

cos^{-1}(*angle*)

**Menu Location**

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

This command works on all calculators.

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`can be used with complex numbers as well.

^{-1}()```
: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