# Math.acosh()

Math.acosh() 函数返回一个数的反双曲余弦值，即：

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

## 语法

Math.acosh(x)

### 参数

x

## 示例

### 使用 Math.acosh()

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：

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


## 规范

Specification
ECMAScript (ECMA-262)
Math.acosh

## 浏览器兼容性

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