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Aug 28, 2017
 #13
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Sadly, melody's way of answering the questions is clumsy and complicated, and takes a lot of time when the numbers get larger (assuming you remember to count every combinations exactly once). This question is a famous one in combinatorics and has a much, MUCH simpler answer than the answers you gave. after reading Jz1234's last post i see he ALMOST got the right answer (and that is VERY impressive, well done!). jz1234's answers works only if we dont mention any upper bound in the question. Let me explain:

 

suppose we have r dices, and suppose every dice has a different color (the dices are distinguishable). The first dice is D1, the second one is D2 and so on. suppose the ith dice has Si sides, and suppose on every side a different integer between 1 to Si is written. We need to find the number of ways we can roll the dices to get the sum A.

 

Jz1234 Realized the number of different rolls is also the number of different solutions to the equation x1+....+xr=A where

0 i i+1. He also realized that the number of solutions to the equations is the number of solutions to the exuation  x 1+....+x r=A-r where 0= i= i-1. Now, Jz1234's solution holds when there is no upper bound S i to any of the dices, and the solution he mentioned can be calculated easily. Sadly this is not the case for the general solution (with upper bounds).

 

suppose Bi- the set containing every combnations of the integers x1, ...., xr where x1+....+xr=A-r and xi>Si-1. Using the inclusion-exclusion principle we can get the solution (https://en.wikipedia.org/wiki/Inclusion%E2%80%93exclusion_principle). 

As far as i know there is no general, nice formula that finds the number of rolls, but that is the best way i can think of for solving this question.

Aug 28, 2017
 #1
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Aug 28, 2017
 #2
avatar+71 
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Aug 28, 2017
 #1
avatar+71 
+1
Aug 28, 2017
 #1
avatar+2446 
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Is the equation \(\sqrt{\sqrt{34}}=\sqrt{c^2}\) in which you want solved? This is what I intepret it as. I will solve it:

 

\(\sqrt{\sqrt{34}}=\sqrt{c^2}\) Square both sides of the equation to get rid of one set of square roots.
\(\sqrt{34}=c^2\) Take the square root of both sides. Of course, taking the square root results in a positive and negative answer.
\(c=\pm\sqrt{\sqrt{34}}\) Now, let's simplify.  \(\sqrt{\sqrt{34}}\)Note that \(\sqrt[n]{a}=a^{\frac{1}{n}}\).
\(\sqrt{\sqrt{34}}=(\sqrt{34})^{\frac{1}{2}}\) Let's use the same principle as above.
\((\sqrt{34})^{\frac{1}{2}}=\left(34^{\frac{1}{2}}\right)^{\frac{1}{2}}\) In the current situation we are in, we will use the rule that \(\left(a^b\right)^c=a^{b*c}\).
\(\left(34^{\frac{1}{2}}\right)^{\frac{1}{2}}=34^{\frac{1}{2}*\frac{1}{2}}=34^{\frac{1}{4}}\) Yet again, we will use the inverse of \(\sqrt[n]{a}=a^{\frac{1}{n}}\) to simplify.
\(c=\pm\sqrt[4]{34}\approx\pm2.4147\)  
   

 

Now, we must check that \(\pm\sqrt[4]{34}\) are valid solutions to this equation. I'll check them separately.

 

\(\sqrt{\sqrt{34}}=\sqrt{c^2}\) Plug in the value of \(\sqrt[4]{34}\) and check its validity.
\(\sqrt{\sqrt{34}}=\sqrt{\left(\sqrt[4]{34}\right)^2}\) This may look complicated, but it can be simplified by realizing that\(\sqrt{a^2}=a\), assuming \(a\geq0\)
\(\sqrt{\sqrt{34}}=\sqrt[4]{34}\) We already calculated earlier than the square root of the square root of a number has a square root index of 4.
\(\sqrt[4]{34}=\sqrt[4]{34}\)  
   

 

Now, let's check the other answer.

 

\(\sqrt{\sqrt{34}}=\sqrt{\left(-\sqrt[4]{34}\right)^2}\) This time, we cannot use the rule we used before because \(-\sqrt[4]{34}<0\). Let's rewrite this as an exponent. 
\(\sqrt{\sqrt{34}}=\sqrt{\left(-34^{\frac{1}{4}}\right)^2}\) Let's use the exponent rule we have used before that states that \(\left(a^b\right)^c=a^{b*c}\). Note that squaring a number automatically makes a number positive, so that is why the negative sign disappears in the next step.
\(\left(-34^{\frac{1}{4}}\right)^2=34^{\frac{1}{4}*\frac{2}{1}}=34^{\frac{2}{4}}=34^{\frac{1}{2}}=\sqrt{34}\) Reinsert this into the equation and compare.
\(\sqrt{\sqrt{34}}=\sqrt{\sqrt{34}}\) This statement is true, as both sides are the same, so both values for c are solutions.
   

 

Therefore, \(c=\pm\sqrt[4]{34}\)

.
Aug 28, 2017
 #2
avatar+753 
+5
Aug 28, 2017

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