---
title: acosd
description: "计算输入实数的反余弦值对应的角度。"
url: https://www.hikunpeng.com/document/detail/zh/hpchistory/hpckit/develop2400/kunpengaccel_kml_0153.html
sourcePath: /source/zh/hpchistory/hpckit/develop2400/kunpengaccel_kml_0153.html
indexId: 4fe7eb873a1e2ba64f443e95ef1de81ac3db7efceb25c76b9702f7a2f4ea3a3667
---
# acosd

计算输入实数的反余弦值对应的角度。

#### 接口定义

C interface：

float acosdf(float x);

double acosd(double x);

long double acosdl(long double x);


#### 参数

| 参数名 | 类型 | 描述 | 输入/输出 |
| --- | --- | --- | --- |
| x | 在acosdf中，x是单精度浮点类型。 在acosd中，x是双精度浮点类型。 在acosdl中，x是长双精度浮点类型。 | 表示输入数据的浮点值。 | 输入 |


#### 返回值

- 返回输入x的反余弦函数值对应的角度y=acos(x) * 180 / π，y ∈ [0, 180]。
- 输入+0，返回90。
- 输入-0，返回90。
- 输入x为1，返回+0。
- 输入x为-1，返回180。
- 输入|x|>1，返回nan。
- 输入±∞，返回nan。
- 输入nan，返回nan。


#### 依赖

C： "km.h"


#### 示例

C interface：

```
// typical usage
    float x1 = -1.0, x2 = 1.0, x3 = 0.5, x4 = -0.5;
    float a = 0.0, b = INFINITY, c = -INFINITY, d = NAN;
    // print result
    printf("acosdf(1.0) = %.15f\n", acosdf(x1));
    printf("acosdf(-1.0) = %.15f\n", acosdf(x2));
    printf("acosdf(0.5) = %.15f\n", acosdf(x3));
    printf("acosdf(-0.5) = %.15f\n", acosdf(x4));
    printf("acosdf(0.0) = %.15f\n", acosdf(a));
    printf("acosdf(-0.0) = %.15f\n", acosdf(-a));
    printf("acosdf(INFINITY) = %.15f\n", acosdf(b));
    printf("acosdf(-INFINITY) = %.15f\n", acosdf(c));
    printf("acosdf(NAN) = %.15f\n", acosdf(d));
    /* 
     * acosdf(1.0) = 180.000000000000000
     * acosdf(-1.0) = 0.000000000000000
     * acosdf(0.5) = 60.000000000000000
     * acosdf(-0.5) = 120.000000000000000
     * acosdf(0.0) = 90.000000000000000
     * acosdf(-0.0) = 90.000000000000000
     * acosdf(INFINITY) = nan
     * acosdf(-INFINITY) = nan
     * acosdf(NAN) = nan
     * 
     * */
```