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Math Forum / Mathematics / Recreational Math / October 2008



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30-60-right triangle properties

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don - 15 Oct 2008 21:38 GMT
Given a 30-60-right triangle with the short leg equal to  x and the
hypotenuse = 2x ...... the question is find the cosine of angles alpha and
beta?

I'm using a book that never gives any answers  :-(     Trigonometry  by I.M.
Gelfand
Greg Neill - 15 Oct 2008 22:14 GMT
> Given a 30-60-right triangle with the short leg equal to  x and the
> hypotenuse = 2x ...... the question is find the cosine of angles alpha and
> beta?
>
> I'm using a book that never gives any answers  :-(     Trigonometry  by I.M.
> Gelfand

You say that it's a 30-60-right triangle?  Then the angles are
specified as 30, 60, and 90 degrees.  So where do alpha and beta
enter the picture?

Anyways, draw a picture, fill in what you know.  Invoke
Pythagorus to find the missing data.  Then read off your
cosines as the appropriate ratios.
don - 15 Oct 2008 23:26 GMT
> So where do alpha and beta
> enter the picture?

Well, according to the standard alpha represents the first angle in a right
triangle and beta represents the second.

http://en.wikipedia.org/wiki/Greek_letters_used_in_mathematics
Greg Neill - 16 Oct 2008 03:04 GMT
>> So where do alpha and beta
>> enter the picture?
[quoted text clipped - 3 lines]
>
> http://en.wikipedia.org/wiki/Greek_letters_used_in_mathematics

A labelling convention need not always be applied.  You simply
have to be specific and consistent in your choices for a
given problem.  To avoid confusion, always spell out your
definitions up front for any given problem.

Did you solve your problem?
don - 16 Oct 2008 05:13 GMT
> Did you solve your problem?

Since the Hypotenuse is 2x and the short leg was x, the sine of alpha would
be .5 indicating a 30 degree angle, leaving the other angle to
be 60, so yes I guess I solved the problem if my thinking is correct... this
damn book never gives an answer......
Michael Stemper - 17 Oct 2008 18:24 GMT
>Given a 30-60-right triangle with the short leg equal to  x and the
>hypotenuse = 2x ......

Are you aware that the hypotenuse of a 30-60-90 triangle will *always*
be twice the length of the short leg?

Signature

Michael F. Stemper
#include <Standard_Disclaimer>
The name of the story is "A Sound of Thunder".
It was written by Ray Bradbury. You're welcome.

 
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