swift trigonometric functions (cos, tan, arcsin, arcos, arctan)

Question

hello I have to differenciate calculations in degrees and I have the following code but I doesn't return me the exact values. The only one right is the value of sin90 in degree = 1

//////***** DEGREES ******//////
var sinus = sin(90.0 * M_PI / 180)
var cosinus = cos(90 * M_PI / 180)
var tangent = tan(90 * M_PI / 180)

var arcsinus = asin(90 * M_PI / 180)
var arcosinus = acos(90 * M_PI / 180)
var arctangent = atan(90 * M_PI / 180)

What is the right operation to return the exact value for every operation in degree for cos, tan and their ARC functions?

`sin` and the rest take _angle in radians_ as an argument. Why do you do this `90 * 180 / M_PI` stuff in the latter part? — 0x416e746f6e, Mar 03 '16 at 11:06
could you write your answer in a piece of code for the value of 90? because I dont really get what you mean .. :) sorry I am new @AntonBronnikov — kepi, Mar 03 '16 at 11:23

Sulthan · Accepted Answer · 2018-07-23T14:02:15.483

50

This is more a math problem than a Swift problem:

let sinus = sin(90.0 * Double.pi / 180)
print("Sinus \(sinus)")

let cosinus = cos(90 * Double.pi / 180)
print("Cosinus \(cosinus)")

let tangent = tan(90 * Double.pi / 180)
print("Tangent \(tangent)")

prints

Sinus 1.0
Cosinus 6.12323399573677e-17
Tangent 1.63312393531954e+16

Sinus of 90 degrees is 1 (correct)

Cosinus of 90 degrees is 0. The value 6e-17 is a very very small value, any sensible rounding would consider it equal to zero (correct). The fact that you can't get exactly zero is due to rounding errors in the calculation.

Tangent of 90 degrees is not defined (sin/tan = 1/0, division by zero is not defined). If we had precise calculations, you would probably get an infinity. In this case we have 1 divided by 6e-17, which becomes a large number 1.6e16. The result is correct.

Regarding the inverse functions, note one thing - their parameters are neither in degrees or radians. Their result is in degrees/radians, for example:

let arcsinus = asin(1.0) * 180 / Double.pi
print("Arcsinus \(arcsinus)")

prints

Arcsinus 90.0

edited Jul 23 '18 at 14:02

answered Mar 03 '16 at 12:14

Sulthan

128,090
22
218
270

so, I do not have to change something? My code is right as it is ? @Sulthan? Any way to return and display the right value on the display? – kepi Mar 03 '16 at 12:18
@kepi Your results are correct, to display them to users, you have to convert them to strings, first. I would recommend `NSNumberFormatter` which will handle rounding and formatting for you. – Sulthan Mar 03 '16 at 12:23
ok @sulthan! Again, I am new so I do not really understand how to implement this NSNumberFormatter ? – kepi Mar 03 '16 at 12:27
1

@kepi There are multiple examples over the internet and stack overflow. Please, search first. – Sulthan Mar 03 '16 at 12:38
What framework you import to access all these function? – Tushar - iOS developer Oct 17 '16 at 12:11
@Tushar-iOSdeveloper If you import `Foundation`, you will have access to all common math functions and constants. – Sulthan Oct 17 '16 at 12:14

score 13 · Answer 2 · answered Jun 18 '18 at 11:04

Swift 4 works out with a modified syntax:

let sinus = sin(90.0 * Double.pi / 180)
let cosinus = cos(90 * Double.pi / 180)
let tangent = tan(90 * Double.pi / 180)

let arcsinus = asin(1) * 180/ Double.pi
let arcosinus = acos(0) * 180/ Double.pi
let arctangent = atan(1) * 180/ Double.pi

swift trigonometric functions (cos, tan, arcsin, arcos, arctan)

2 Answers2