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director cosines

malmeida2019
7-Bedrock

director cosines

Good morning friends of the group, sorry if my questions are easy, but I'm new to Mathcad. I don't know how to solve this type of equation, I would like the answer to be in degrees.The answer must be 120º.

 

 

 

 

 

 

 

 

 

 

ACCEPTED SOLUTION

Accepted Solutions
Cornel
19-Tanzanite
(To:malmeida2019)

Cornel_0-1695912425835.png

Cornel_1-1695912432464.png

So, the answer seems to be 45 deg (at least with your above given equation for calculating Cornel_2-1695912932123.png), not 120 deg...

Are you sure that the answer must be 120 deg?

 

Cornel_0-1695912719469.png

Cornel_0-1695913296250.png

 

 

So, the correct formula for y2 is:

Cornel_0-1695913822548.png

Cornel_2-1695913865882.png

where:

Cornel_1-1695913839485.png

View solution in original post

6 REPLIES 6
Cornel
19-Tanzanite
(To:malmeida2019)

Cornel_0-1695912425835.png

Cornel_1-1695912432464.png

So, the answer seems to be 45 deg (at least with your above given equation for calculating Cornel_2-1695912932123.png), not 120 deg...

Are you sure that the answer must be 120 deg?

 

Cornel_0-1695912719469.png

Cornel_0-1695913296250.png

 

 

So, the correct formula for y2 is:

Cornel_0-1695913822548.png

Cornel_2-1695913865882.png

where:

Cornel_1-1695913839485.png

TKS

3.png

Cornel
19-Tanzanite
(To:malmeida2019)

Your calculation formula for y2 in your Mathcad file was wrongly derived...see my above post

Some additional remarks:

The symbolics does not know anything about units, it does not know deg or °. This is the reason why the symbolic result shown on Cornels answer still includes the expressions cos(60°), etc.

If you like you can redefine the used units at the top of the sheet (maybe in a collapsed region)

Werner_E_0-1695921058817.png

Now the symbolic result looks less ugly (and of course its in radian, not degree)

Werner_E_1-1695921131753.png

Your equation has an infinite number of solutions and if you know in which range you are looking for the solution (maybe between 90° and 180 °) you can tell Primes symbolics (using the "assume" modifier) to give you just the needed solution

Werner_E_2-1695921380589.png

If you have (re)defined the unit ° as explained above, you can also use degree in the assume modifier (the result will always be shown in radiant)

Werner_E_3-1695921460361.png

 

 

 

 

 

thank my friend for the brilliant explanation. Thank you 

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