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ascozzarella1-Visitor
1-Visitor
March 12, 2016
Question

Mathcad and irrational symbolic trigonometrics

  • March 12, 2016
  • 5 replies
  • 2285 views

Hi,

I'm a newby with Mathcad Prime and I'd like to know how can I use trigonometrics symbolism, ie 90 degrees angle like pi/2 or cos of 0.36 radians like 3 times square root of 73 fraction 73 and so on.

Mathcad returns me the approximate decimal numbers and not the symbolic fraction or the symbolic pi.

Thanks in advance

5 replies

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LucMeekes23-Emerald IV
23-Emerald IV
March 14, 2016

So you do not get answers like these:

?

What does it show for you?

Luc

V
24-Ruby IV
ValeryOchkov24-Ruby IV
24-Ruby IV
March 14, 2016

Angelo Scozzarella написал(а):

Hi,

I'm a newby with Mathcad Prime and I'd like to know how can I use trigonometrics symbolism, ie 90 degrees angle like pi/2

Thanks in advance

But better use Maple or Mathematica

W
Werner_E25-Diamond I
25-Diamond I
March 14, 2016

1) Whenever Mathcads symbolics encounter a decimal point it switches to float mode and provides approximate results.

This is very annoying and undesirable but there is nothing you can do but taking care not to use the decimal point, writing 0.36 as 36/100, etc.

2) Mathcads symbolics does not know anything about units and so it does not know what degrees is. You can tell it the symbolic by (re)definig deg

3) You will have to be more specific as to what you intend to calculate and what you want to see.

Just give concrete examples what you are trying to do and there mioght be a way to accomplish it.

BTW cos (0.36) for sure equals NOT 3*sqrt(73)/73 or did you mean something else?

WE

A
ascozzarella1-VisitorAuthor
1-Visitor
March 14, 2016

Thank you very much for answers.

First of all I'm very sorry for having change sin and cos.

3*sqrt(73)/73 is the sin (0.36).


So, according your advices, I should insert as input not decimal values.


Well, I'll try.


Other suggestions will be wellcome.

W
Werner_E25-Diamond I
25-Diamond I
March 14, 2016

First of all I'm very sorry for having change sin and cos.

3*sqrt(73)/73 is the sin (0.36).

Sure not! At best its a coarse approximation

or the other way round

Thats not (exactly) 0,36

Why do you think that the sine of 0,36 is that value?

If you have a right-angled triangle with the cathetus 3 and 8, one of the angles is alpha=arctan(3/8). alpha is approximately 0,36, but the exact "value" is arctan(3/8) - its an irrational number. And the sine of that angle alpha is NOT sin(0.36) but is sin(arctan(3/8)) which Mathcad will happily calculate as

or that way

Don't use inline evaluation like

as this will store a numerical approximation in alpha and the symbolics will not be able to recover the exact value

WE

A
ascozzarella1-VisitorAuthor
1-Visitor
March 15, 2016

Thank you again Werner.

Now it's all more clear and I've got a better vision about MathCad works.

The strange fraction as sin of the .36 radians angle is into an old trigonometrics tables book.

W
Werner_E25-Diamond I
25-Diamond I
March 15, 2016

The strange fraction as sin of the .36 radians angle is into an old trigonometrics tables book.

Presumably an 3 - 8 right angled triangle, where one angle is approximately 0.36, as shown above.

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