files/en-us/web/javascript/reference/global_objects/math/asin/index.md

metadata

title: Math.asin()
short-title: asin()
slug: Web/JavaScript/Reference/Global_Objects/Math/asin
page-type: javascript-static-method
browser-compat: javascript.builtins.Math.asin
sidebar: jsref

The Math.asin() static method returns the inverse sine (in radians) of a number. That is,

$$\forall x∊[-1,1],𝙼𝚊𝚝𝚑.𝚊𝚜𝚒𝚗(𝚡)=arcsin(x)=\text{the unique }y∊\left[-\frac{\pi }{2},\frac{\pi }{2}\right]\text{ such that }sin(y)=x\backslash forall\; x\; \backslash in\; [\{-1\},\; 1],\backslash ;\backslash mathtt\{\backslash operatorname\{Math.asin\}(x)\}\; =\; \backslash arcsin(x)\; =\; \backslash text\{the\; unique\; \}\; y\; \backslash in\; \backslash left[-\backslash frac\{\backslash pi\}\{2\},\; \backslash frac\{\backslash pi\}\{2\}\backslash right]\; \backslash text\{\; such\; that\; \}\; \backslash sin(y)\; =\; x$$

{{InteractiveExample("JavaScript Demo: Math.asin()")}}

// Calculates angle of a right-angle triangle in radians
function calcAngle(opposite, hypotenuse) {
  return Math.asin(opposite / hypotenuse);
}

console.log(calcAngle(6, 10));
// Expected output: 0.6435011087932844

console.log(calcAngle(5, 3));
// Expected output: NaN

Syntax

Math.asin(x)

Parameters

• x
  • : A number between -1 and 1, inclusive, representing the angle's sine value.

Return value

The inverse sine (angle in radians between $-\frac{\pi }{2}-\backslash frac\{\backslash pi\}\{2\}$ and $\frac{\pi }{2}\backslash frac\{\backslash pi\}\{2\}$, inclusive) of x. If x is less than -1 or greater than 1, returns {{jsxref("NaN")}}.

Description

Because asin() is a static method of Math, you always use it as Math.asin(), rather than as a method of a Math object you created (Math is not a constructor).

Examples

Using Math.asin()

Math.asin(-2); // NaN
Math.asin(-1); // -1.5707963267948966 (-π/2)
Math.asin(-0); // -0
Math.asin(0); // 0
Math.asin(0.5); // 0.5235987755982989 (π/6)
Math.asin(1); // 1.5707963267948966 (π/2)
Math.asin(2); // NaN

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

• {{jsxref("Math.acos()")}}
• {{jsxref("Math.atan()")}}
• {{jsxref("Math.atan2()")}}
• {{jsxref("Math.cos()")}}
• {{jsxref("Math.sin()")}}
• {{jsxref("Math.tan()")}}
• CSS {{cssxref("asin()")}} function