The ACOS Function returns the inverse cosine of a number in radians. The number must be between -1 and 1.

If the number is outside -1 to 1, Excel will return a #NUM error.

**Syntax:**

**=acos(number)**

**Arguments:**

**number**– Number between -1 and 1.

**PV Function Usage Example:**

Below is an example of how to use the ACOS Function. In the below example, we are looking for the inverse cosine of .85 and -.65. The result in radians in shown below.

A Radian is a unit of angle, equal to an angle at the center of a circle whose arc is equal in length to the radius. Please see the slide below.

**Syntax:**

**=ACOS(.85)
Result: 0.554811033 Radians**
**=ACOS (-.65)
Result: 2.278380764 Radian**

## Radian to Degrees

**Syntax:**

**=DEGREES(ACOS(-0.65))**
**=ACOS(-0.65)*180/PI()**

You can easily convert the returned Radian from the ACOS function to degrees by using the DEGREES function and PI function as shown below.

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