How do i use Math.sin() in javascript to get correct answer?

Question

When I use Math.sin(90) for calculating Sine of 90 degrees in javascript it returns 0.8939966636005565, but sin(90) is 1. Is there a way to fix that? I need accurate values for any angle.

<!DOCTYPE html>
<html>
<body>
    <p id="demo">Click the button calculate value of 90 degrees.</p>
    <button onclick="myFunction()">Try it</button>
<script>
function myFunction(){
    document.getElementById("demo").innerHTML=Math.sin(90);
}
</script>

The trig functions in JavaScript operate on radians, not degrees. — Pointy, Mar 30 '14 at 14:36
@Pointy Possible duplicate, i didn't know it works in radians. — JaSamSale, Mar 30 '14 at 14:48

score 15 · Accepted Answer · answered Mar 30 '14 at 14:36

15

Math.sin expects the input to be in radian, but you are expecting the result of 90 degree. Convert it to radian, like this

console.log(Math.sin(90 * Math.PI / 180.0));
# 1

As per the wikipedia's Radian to Degree conversion formula,

Angle in Radian = Angle in Degree * Math.PI / 180

answered Mar 30 '14 at 14:36

thefourtheye

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3

How come `console.log(Math.sin(180 * Math.PI / 180));` returns `1.2246467991473532e-16` instead of `0`? – nils Jul 28 '15 at 08:20
3

@nils - Notice that the number `1.2246467991473532e-16` is very very small, and It is equivalent to `0.00000000000000012246467991473532` (notice the `e-16`) at the end of the number, which is a scientific form of writing a number. – Greeso Nov 27 '17 at 21:20

score 6 · Answer 2 · answered Mar 30 '14 at 14:37

6

The sin function in Javascript takes radians, not degrees. You need to convert 90 to radians to get the correct answer:

Math.sin(90 * (Math.PI / 180))

answered Mar 30 '14 at 14:37

sjf

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How do i use Math.sin() in javascript to get correct answer?

2 Answers2