Another suggestion for the unused keys

discussion of the scientific/engineering emulator
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Billf
Posts: 5
Joined: Wed Jan 11, 2012 4:05 pm

Another suggestion for the unused keys

Post by Billf » Sat Jan 28, 2012 4:17 pm

Another possible use for the five unused keys are a triangle solver. Solving triangles is useful in surveying, construction, and possibly navigation. However triangles are a little tricky to solve requiring either the law of sines or the law of cosines.

Background

The sides of triangles are normally labeled "a", "b", and "c" while the vertexes are labeled "A", "B", "C". Vertex "C" is opposite side "c". Said differently, vertex "C" is the vertex between sides "a" and "b".

The Triangle solver has a total of 6 memories: Angle A, angle B, angle C, side a, side b, and side c.

The keys

Four of the buttons would be labeled "Angle", "a", "b", "c"

Pressing the ["a"] key stores the contents of the X register in the "side a" memory.
Pressing the [Angle] ["a"] keys store the contents of the X register in the "Angle A" memory.

Once the user has entered values for three of the registers, the calculator would calculate the values of the remaining sides and angles. For example, if the user enters values for side a, angle B, and side c then the calculator would calculate the values for angle A, side b, and angle C.

You retrieve the values the registers by pressing the [RCL] key. For instance, to retrieve the value of side a, press [RCL] ["a"]. To retrieve the value of angle B, enter [RCL] [Angle] ["b"].

If the user enters a new value for one of the memories, all remaining memories will be recalculated based on the new value. For instance:

Suppose a user enters a value for sides "a", "b", and angle "B", the remaining sides will be recalculated based on these values. If the user then enters a new value for side "b", all remaining values will be computed based on the new values for sides "a", "b", and angle "B".

Suppose a user enters values for sides "a", "b", and angle "B" and then enters a value for side "c". All remaining values would be computed based on the user entered values for side "b", angle "B", and side "c" because these are the last three values specified by the user.

Note that there are a number of situation where a triangle cannot be computed. These include situations where only three angles are supplied, or that the values of the supplied angles exceed 180 degrees, or that the length of one side is longer than the length of the other two sides added together.

In situations where angle "A" and sides "b" and "c" are supplied there might be zero, one, or two solutions.

Related functions that would be useful:

"d.mmss+" and "d.mmss-" These functions assume that the values in both the X and Y registers are degrees-minutes-seconds-fraction of second and adds X to Y or subtracts X from Y.

"Normalize" converts the value in the X register to a value between 0 and 360 degrees or 0 and 2-PI depending on whether the calculator is in Degrees or Radians mode. This is done by adding or subtracting a multiple of 360 as appropriate.

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