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Consider the following triangle :

enter image description here

I want to calculate angle X

I have the following :

    var opposite = 2.5;
    var hypotenuse = 5;

    var sinOfAngleX = opposite / hypotenuse; // 0.5

So now I know that Math.sin(valueofAngleX) would return 0.5.

But how do I get the value of an angle if I know the sine of the angle, using the Math() library?

According to this tutorial, I need to do :

var angleX = sin to the power of negative one of 0.5

but I don't know how to translate that into JS.

I tried :

var angleX = Math.pow(Math.sin(sinOfAngleX), -1);

but it returns 2.085829642933488 which is obviously wrong. The correct answer should be 30

And in case all of the above is wrong to begin with, does anyone know how I can calculate angle X correctly using the JS Math() library?

Thanks!

Kawd
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  • At the very least, it looks like you're taking the sine of the sineOfAngleX, which is wrong to start with. (thanks whoever -1'd me, I meant that to be a comment rather than an answer) – Paul Jan 05 '15 at 17:45
  • `sin^-1(a)` here does not mean `1/sin(a)`, but rather `"the inverse function of sin"(a)`, thus arcsin (a.k.a. `asin`). To write `1/sin(a)` with `^-1`, one would add parenthesis : `(sin(a))^-1`. Note that `sin(a^-1)` means `sin(1/a)`, and `sin(a)^-1` is ambiguous, thus should be avoided. – Cimbali Jan 06 '15 at 00:56

2 Answers2

20

You can know the angle of any sin with this formula:

Math.asin(sinOfAngleX) * 180/Math.PI

With sinOfAngleX = 0.5, Math.asin(sinOfAngleX) would give 0.5235987755982989. This is expressed in radians. To pass it to degrees you can multiply by 180/Math.PI, which results in 30º

Umagon
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-1

In ES6 you can use the build it method from Math Object

 Math.hypot(3, 4)

enter image description here

ALLSYED
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    Good code trick, however, that actually gives you the length of the hypotenuse, not the angle asked for in the OP. – Steve Oct 08 '16 at 04:30