# Math.acosh()

## BaselineWidely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

Math.acosh() 函数返回一个数的反双曲余弦值，即：

$∀ x ≥ 1 , Math.acosh ( x ) = arcosh ( x ) = the unique y ≥ 0 such that cosh ( y ) = x \forall x \geq 1, \mathtt{\operatorname{Math.acosh}(x)} = \operatorname{arcosh}(x) = \text{ 唯一的} ; y \geq 0 ; \text{使得} ; \cosh(y) = x$

## 语法

js
Math.acosh(x)


### 参数

x

## 示例

### 使用 Math.acosh()

js
Math.acosh(-1); // NaN
Math.acosh(0); // NaN
Math.acosh(0.5); // NaN
Math.acosh(1); // 0
Math.acosh(2); // 1.3169578969248166


## 向下兼容

$x \geq 1$ 时，都有 $\operatorname \left\{arcosh\right\} \left(x\right) = \ln \left\left(x + \sqrt\left\{x^\left\{2\right\} - 1\right\} \right\right)$ ，因此可以使用以下函数实现：

js
Math.acosh =
Math.acosh ||
function (x) {
return Math.log(x + Math.sqrt(x * x - 1));
};


## 规范

Specification
ECMAScript Language Specification
# sec-math.acosh

## 浏览器兼容性

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