Re: high school trigonometry?





Solid State 80 wrote:

Dray the joints and do the math -- nothing more that simple analytic trigonometry is required.

I did just that. And from your Google advice and the other responder's other links I have some promising leads and more geometry/trigonometry challenges.

But there remains the matter of the formula my methods came up with, and the fact that it gives good answers, modulo a supplementary angle here and there.

In developing the miter angle, for example, I had an intermediate expression

Cos[Theta]^2 / Sin[Phi]^2 + Sin[Theta]^2 - 1

which yielded nicely to the use of cos^2 x + sin^2 x = 1, giving me

Cos[Theta]^2 / Tan[Phi]^2

Hence my belief that my expression for the bevel angle could also be, er, improved.

Leave the carpentry out of it! Since the expression

ArcCos[ Cos[Theta]^2 Sin[Phi] + Sin[Theta]^2 ]

seems to work like

bladeTilt = ArcSin[Sin[B] Sin[A/2]]

I think the uglier expression could be simplified using other trigonometric manipulations.

How can I get from something like

Cos[Theta]^2 Sin[Phi] + Sin[Theta]^2

to

Sin[B] Sin[A/2]

Where Theta has a simple relation to B and Phi is simply related to A?

Meanwhile I will try again from first principles other approaches to the derivation of the simple formula on all the carpentry websites.

--
rob
.



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