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 #5
avatar+1009 
-5
Mar 20, 2019
 #1
avatar+26388 
+5

2015 SS 28

 

1.

cos-theorem:

\(\begin{array}{|rcll|} \hline BM^2&=&x^2+\left(\dfrac{x}{2}\right)^2-2\cdot x \cdot \dfrac{x}{2}\cos(108^\circ) \\ BM^2 &=& x^2\left(1+\dfrac{1}{4}-\cos(108^\circ)\right) \quad |\quad \cos(108^\circ)=\cos(180^\circ-72^\circ)=-\cos(72^\circ) \\ BM^2 &=& x^2\left( \dfrac{5}{4}+\cos(72^\circ)\right) \\ \mathbf{BM} &\mathbf{=}& \mathbf{x \sqrt{\dfrac{5}{4}+\cos(72^\circ)}} \\ \hline \end{array} \)

 

2.
sin-theorem:

\(\begin{array}{|rcll|} \hline \dfrac{\sin(z)}{x} &=& \dfrac{\sin(36^\circ)}{ZB} \\\\ \mathbf{ZB} &\mathbf{=}& \mathbf{\dfrac{\sin(36^\circ)}{\sin(z)}x }\\ \hline \end{array} \)

 

3.

sin-theorem:

\(\begin{array}{|rcll|} \hline \dfrac{\sin(180^\circ-z)}{\frac{x}{2}} &=& \dfrac{\sin(72^\circ)}{ZM} \\\\ \dfrac{2\sin(z)}{x} &=& \dfrac{\sin(72^\circ)}{ZM} \\\\ \mathbf{ZM} &\mathbf{=}& \mathbf{\dfrac{\sin(72^\circ)}{2\sin(z)}x }\\ \hline \end{array} \)

 

\(\mathbf{z=\ ?}\)

\(\begin{array}{|rcll|} \hline BM &=& ZB+ZM \\ BM&=& \dfrac{\sin(36^\circ)}{\sin(z)}x+\dfrac{\sin(72^\circ)}{2\sin(z)}x \\\\ BM&=& \dfrac{x}{\sin(z)} \left( \sin(36^\circ) + \dfrac{\sin(72^\circ)}{2}\right) \quad | \quad BM=x \sqrt{\dfrac{5}{4}+\cos(72^\circ)} \\\\ x \sqrt{\dfrac{5}{4}+\cos(72^\circ)}&=& \dfrac{x}{\sin(z)} \left( \sin(36^\circ) + \dfrac{\sin(72^\circ)}{2}\right) \\\\ \sqrt{\dfrac{5}{4}+\cos(72^\circ)}&=& \dfrac{1}{\sin(z)} \left( \sin(36^\circ) + \dfrac{\sin(72^\circ)}{2}\right) \\\\ \mathbf{\sin(z)} & \mathbf{=} & \mathbf{ \dfrac{ \sin(36^\circ) + \dfrac{\sin(72^\circ)}{2} }{\sqrt{\dfrac{5}{4}+\cos(72^\circ)}} } \\\\ z &=& 180^\circ- \arcsin\left( \dfrac{ \sin(36^\circ) + \dfrac{\sin(72^\circ)}{2} }{\sqrt{\dfrac{5}{4}+\cos(72^\circ)}}\right) \\ &=& 180^\circ- \arcsin\left( \dfrac{ 1.06331351044 }{1.24860602048} \right) \\ &=& 180^\circ- \arcsin\left( 0.85160049928 \right) \\ &=& 180^\circ- 58.3861775592^\circ \\ \mathbf{z} &\mathbf{=}& \mathbf{121.613822441^\circ} \\ \hline \end{array}\)

 

\(\text{Let $\angle ABM =180^\circ-(36^\circ+z) $} \\ \text{Let $ 36^\circ+z = 36^\circ+ 121.613822441^\circ=157.613822441^\circ$} \)

 

4.
sin-theorem:

\(\begin{array}{|rcll|} \hline \dfrac{\sin(z)}{x} &=& \dfrac{\sin(ABM)}{3} \quad | \quad \angle ABM =180^\circ-(36^\circ+z) \\\\ \dfrac{\sin(z)}{x} &=& \dfrac{\sin\Big(180^\circ-(36^\circ+z)\Big)}{3} \\\\ \dfrac{\sin(z)}{x} &=& \dfrac{\sin( 36^\circ+z )}{3} \\\\ \mathbf{x} &\mathbf{=}& \mathbf{3\cdot \dfrac{\sin(z)}{\sin( 36^\circ+z )} } \\\\ x & = & 3\cdot \dfrac{0.85160049928}{\sin( 157.613822441^\circ )} \\\\ x & = & 3\cdot \dfrac{0.85160049928}{0.38084732121} \\\\ x & = & 3\cdot 2.23606797751 \quad | \quad 2.23606797751 = \sqrt{5} \\ \mathbf{x} &\mathbf{=}& \mathbf{3\cdot \sqrt{5}} \\ \hline \end{array}\)

 

laugh

Mar 20, 2019
 #7
avatar+2490 
+2

Now correct me if I'm wrong but this site people come to to get answers. (sic)

 

Well ... yes, it is. I’m sure it wasn’t the creator’s original intent, but over time, it’s morphed into a homework answer and a defacto “cheating” forum. Diligent students can certainly learn from this, but for most, it presents only an illusion of knowledge, with no real substance of learning.     

 

... Anyone can come to this site and post questions as well as answers..  Nowhere does it state that you are obligated to even click on my question. Muchless read it or even answer it!! (sic)

 

Yep; you’ve summed it up in three generalized, poorly punctuated, sentences. 

 

Instead of wasting our time you can simply move on along, leave me alone, quit wasting MY time!!  (sic)

 

Yes, I could simply have moved on, and you could have simply pursued further explanation on your original post rather than repeatedly posting the same question with the expectation that someone will present a solution that magically gives you an understanding of the prerequisite concepts. 

 

Your comments on your pervious post indicated a sincere desire to learn this material.   So I spent the time to present detailed information on where you can learn the techniques to solve that particular type of statistical problem and where to learn the prerequisite concepts.  That took about 60 minutes to research, verify, and post –well longer than the five minutes needed to just answer this simple question.   (No comments about this; just bitching about harsh bullying.)

 

I then see this post, with your repeated question and a lament about three different answers.  I then knew with certainty that the time I invested in responding to your question was wasted.   So I trolled your lame and lazy ass. That pissed you off, so I at least recovered something from my investment of time. 

 

BTW, I am not a guy.   Most children –even very young children know this. But maybe you lack the prerequisites for this subject, too.  Do you need links that will help in gender recognition?  ...Meh, that’s just a waste of time.indecision 

 

GA

Mar 20, 2019
 #1
avatar+37159 
0
Mar 20, 2019

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