In addition, "vertical" length and "horizontal" length sort of narrows
it down to a right triangle.

Another interesting rule of thumb:  For small angles the sine, tangent,
and angle are all the same.  (The angle is measured in radians rather
than degrees.  There are 2*pi radians in 360 degrees.)  The smaller the
angle the more accurate the rule of thumb.

For Georges problem:
tangent is 3/30 = .1
sine is 3/30.1496 = .09950 (denominator from Pythagorean theorem)
angle in degrees is 5.71059 (from the arc tangent)
   so in radians it is 2*pi (5.71059/360) = .099669

and the difference between them is less than 0.5 %.

Bob W.


On Sat, 12 Jan 2008 07:25:53 -0700
Dale Rogers <dale.r@cox.net> wrote:

But Joe, any triangle can be divided into two right triangles.

Dale R.

Joe Ewen wrote:
> For those who may use this formula, this formula will only work on a
> right triangle.  Please correct me if I am wrong.
> Joe
>
>
>
>     ----- Original Message -----
>     *From:* Ed Anderson <mailto:eanderson@carolina.rr.com>
>     *To:* Rotary motors in aircraft > <mailto:flyrotary@lancaironline.net>
>     *Sent:* Saturday, January 12, 2008 8:30 AM
>     *Subject:* [FlyRotary] Re: Angles
>
>     Hi George,
>
>     Several folks have responded to your question concerning angles,
>     for what it is worth I also got 5.729 degrees.
>
>     There are a couple of formulas you can use.  One common approach
>     is to use
>     ArcSin, but unless you have a convenient ArcSin function available
>     that can be problematic.
>
>     So instead I like to use this one for y/r (y being the vertical
>     length of your angle and r the horizontal length)   Degrees = y/r
>     * 180/pi   = 3/30*180/3.1456 =  5.729 deg.  This way you don't
>     need a table/function of ArcSin.
>
>     Ed
>
>


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